opinion: Mr. Justice Black
  delivered the opinion of the Court.
  In 1952 the State of Arizona invoked the' original jurisdiction of this Court by filing a complaint against' the State of California and seven of its public agencies. Later, Nevada, New Mexico, Utah, and the United States; were added as parties either voluntarily or on motion. The basic controversy in the case is over how much water each State has a legal right to use out of the waters of the Colorado River and its tributaries. After preliminary pleadings, we referred the case to ■ George I. Haight; Esquire, and upon his death in 1955 to Simon H. Rif kind,. Esquire, as Special Master to take evidence, find facts, state- conclusions of law, and recommend a decree, all “subject to consideration, revision, or approval by the Court.” The Master conducted a trial lasting from June 14, 1956, to August 28, 1958, during which 340 witnesses were heard orally or by deposition, thousands of exhibits were received, and 25,000 pages of transcript were filled. Following many motions, arguments, and briefs, the Master in a 433-page volume reported his findings, conclusions, and recomménded decree, received by the Court on January 16,1961. The case has been extensively briefed here and orally argued twice, the first time about 16 hours, the second, over six. As we see this case, the question of each State’s share of the waters of the Colorado and its tributaries turns on the meaning and the scope of the Boulder Canyon Project Act passed by Congress in 1928. That meaning and scope can be better understood when the Act is set against its background — the gravity of. the Southwest's water problems; the inability of local groups or individual States to deal with these enormous problems; the' continued failure of the States to agree on how to conserve and divide the waters; and the ultimate action by Congress at the request of the States creating a .-great system of dams and public works nationally built, controlled, and operated for the purpose of conserving and distributing the' water.
  The Colorado River itself rises in the mountains of Colorado and flows generally in a southwesterly direction for about 1,300 miles through Colorado, Utah, and Arizona and along the Arizona-Nevadá and Arizona-California boundaries, after which it passes into Mexico and empties into the Mexican waters of the Gulf of California. On its way to the sea it receives tributary waters from Wyoming, Colorado, Utah, Nevada, New Mexico, and Arizona. The' river and its tributaries flow in a natural basin almost surrounded by large mountain ranges and drain 242,000 square miles, an area about 900 miles long from north to south and 300 to 500 miles wide from east to west — practically one-twelfth the area of the continental United States excluding Alaska. Much of this large basin is so arid that it is, as it always has been, largely dependent upon managed use of the.waters of the Colorado River System to make it productive and inhabitable. The Master refers to archaeological evidence .that as long as 2,000 years ago the ancient Hohokam tribe built and maintained irrigation canals near what is now Phoenix, Arizona, and that American Indians were practicing irrigation in that region at the time white men first explored it. In the second half of the nineteenth century a group of people interested in California’s Imperial Valley conceived plans to divert water from the mainstream of the Colorado to give life and growth to the parched and barren soil of that valley. As the most feasible route was through Mexico, a Mexican corporation was formed and a canal dug partly in Mexico and partly in the United States. Difficulties which arose because the canal was subject to the sovereignty of both countries generated hopes in this country that some day there would be a canal wholly within the United States, an all-American canal.
  During the latter part of the nineteenth and the first part of the twentieth centuries, people in the Southwest continued to seek new ways to satisfy their water needs, which by that time were increasing rapidly/as new settlers moved into this fast-developing region. ,But none of the more or less primitive diversions made from the mainstream of the Colorado conserved enough water to meet the growing needs of the basin. The natural flow of the Colorado was too erratic', the river at many places in canyons too deep, and the engineering and economic hurdles too great for small farmers, larger groups, or even States to build storage dams, construct canals, and install the expensive works necessary for a dependable year-round water supply. Nor were droughts the basin’s only problem; spring floods due to melting snows and seasonal storms were a recurring menace, especially disastrous in California’s Imperial Valley where, even after the Mexican canal provided a more dependable water supply, the threat of flood remained at least as serious as before.. Another troublesome problem was the erosion of land' and the deposit of silt which fouled waters, choked irrigation works, and damaged good farmland and crops.
  It is not surprising that the pressing necessity to transform the erratic and often destructive flow of the Colorado River into a controlled and dependable water supply desperately needed in so many States began tó be talked about and recognized as far more than a purely -local problem which could be solved on a farmer-by-farmer, group-by-group, or even state-by-state basis, desirable as this kind of solution might have been.' The inadequacy of a local solution was recognized in the Report of the All-American Canal Boarc] of the United' States Department of the Interior on July 22, 1919, which detailed the widespread benefits that could be expected from construction by the United States of a large reservoir on the mainstream of the Colorado and an all-American canal to the Imperial Valley. Some months later, May 18, 1920, Congress passed a bill offered by Congressman Kinkaid of. Nebraska directing the Secretary of the Interior to make a study and report of diversions which might be made from the Colorado River for irrigation in the Imperial Valley. The Fall-Davis Report, submitted to Congress in compliance .with the Kinkaid Act, began by declaring, “The control of the floods and' development of the resources of the Colorado River are peculiarly national problems . . .” and then went on to give reasons why this was so, concluding with the statement that the job was so big that only the Federal Government could do it. Quite naturally, .therefore, the Report recommended that the United States construct as a government project not only an alLAmerican canal from the Colorado River to the Imperial Valley but also a dam and reservoir at or near Boulder Canyon.
  The prospect that the United States .would undertake to build as a national project the necessary works to control floods and store river -waters for irrigation was apparently a welcome one for the basin States. But it brought to life strong fears in the northern basin States that additional waters made available by the storage and canal projects might be gobbled up in perpetuity by faster growing lower basin areas, particularly California, before the upper States could appropriate what they believed to be their fair share. These fears were not without foundation,. since the law of prior appropriation prevailed in most of the Western States, Under that law the One who first appropriates water and puts it to beneficial use thereby acquires a vested right to continue to divert and use that quantity of water against, all claimants junior to him in point of time. “First in time, first in right” is the shorthand expression of this legal principle. In 1922, only four months after the Fall-Davis Report, this Court in Wyoming v. Colorado, 259 U. S. 419, held that the doctrine of prior appropriation could be given interstate effect. This decision intensified fears of Upper Basin States that they would not get their fair share of Colorado River water. In view of California’s '.phenomenal growth, the Upper Basin States had particular reason to fear that California, by appropriating and. using Colorado River water before the upper States, would', under the interstate application of the prior appropriation doctrine, be “first in time” and therefore “first in right.” ' Nor were such fears limited to the northernmost States. Nevada, Utah, and especially Arizona .were all apprehensive that California’s rapid declaration of appropriative claims would deprive them of their just share of basin water available after construction of the proposed United States project. It seemed for a time that these fears would keep the States from agreeing- on any kind of division of the river waters. Hoping to prevent “conflicts” and “expensive litigation” which would hold up or prevent the tremendous benefits expected from extensive federal development of the river, the basin States requested and Congress passed an Act on August 19, 1921,- giving the States consent to negotiate and enter into a compact for the “equitable division and apportionment ... of the water supply of the Colorado River.”
  Pursuant to -this congressional authority, the seven States appointed Commissioners who, after negotiating for the better part of a year, reached an agreement at Santa Fe, New Mexico, on November 24, 1922. The ágreement, known as the Colorado River Compact, failed to fulfill the hope of Congress that the States would themselves agree on each State’s share of the water. The most the Commissioners were able to accomplish in the Compact was to adopt a compromise suggestion of Secretary of Commerce Herbert Hoovér, specially designated as United States representative. This, compromise divides the entire basin into two parts, the Upper Basin and the Lower Basin, separated at a point on the river in northern Arizona known as Lee Ferry. (A map showing the two basins and other points of interest in this controversy is printed as an Appendix facing p./602.) Article III (a) of the Compact apportions to each basin in perpetuity-7,500,000 acre-feet of water a year from the Colorado River System, defined in Article II (a) as “the Colorado River and its tributaries within' the United States of America.” In addition, Article III (b) gives the Lower Basin “the right to increase its beneficial consumptive use of such waters by one million acre-féet per annum.” Article III.(c) provides that future Mexican water rights recognized by the United States shall be supplied first out of surplus over and above the aggregate of the quantities specified in (a) and (b), and if this surplus is not enough the deficiency shall be borne equally by the two basins. Article III (d) requires the Upper Basin not to deplete the Lee Ferry flow below an aggregate- of 75,000,000 acre-feet for any 10 consecutive years. Article III (f) and (g) provide a way for further apportionment by a compact of “Colorado River System” waters at any time after October 1, 1963. While these allocations quieted rivalries between the Upper and Lower Basins, major differences between the States in the Lower Basin continued. Failure of the Compact to determine each State’s share of the water left Nevada and Arizona with their fears that the law of prior appropriation would be not a protection but a menace because California-could use that law to get for herself the lion’s share of the waters allotted to the Lower Basin. Moreover, Arizona, because of her particularly strong interest in the Gila, intensely resented the Compact’s inclusion of the Colorado River tributaries in its allocation scheme and was bitterly hostile to having Arizona tributaries,' again particularly the Gila, forced to contribute to the Mexican burden. Largely for these reasons, Arizona alone, of all the States in both basins, refused to ratify the Compact.
  Seeking means which would permit ratification by all seven basin States, the Governors of those States met at Denver in 1925 and again in 1927. As a result of these meetings the Governors of the upper States suggested, as a fair apportionment of water among the Lower Basin States, that out of the average annual delivery of water at Lee Ferry required by the Compact — 7,500,000 acre-feet— Nevada be given 300,000 acre-feet, Arizona 3,000,000, and California 4,200,000, and that unapportioned waters, subject to reapportionment after 1963, be shared equally by Arizona and California. Each Lower Basin State would have “the exclusive beneficial consumptive use of such tributaries within its boundaries before the same empty into thé main stream,” except that Arizona tributary waters in excess of '1,000,000 acre-feet could under some circumstances be subject to diminution by reason of a United States treaty with Mexico. This proposal foundered because California held out for 4,600,000 acre-feet instead of 4,200,000 and because Arizona held out for complete exemption of its tributaries from any part of the Mexican burden.
  Between 1922 and 1927 Congressman Philip Swing and Senator Hiram Johnson, both of California, made three attempts to have Swing-Johnson bills enacted, authorizing construction of a dam in the canyon section of the Colorado River and an all-American canal. These bills would have carried put the original Fall-Davis Report’s recommendations that the river problem be recognized and treated as national, not local. Arizona’s Senators and Congressmen, still insisting upon a definite guaranty of water from the. mainstream,-, bitterly fought these proposals because they failed to provide for exclusive use of her own tributaries, particularly the Gila, and for exemption of these tributaries from the Mexican burden.
  Finally, the fourth Swing-Johnson bill passed both Houses and became the Boulder Canyon Project Act of December 21, 1928, 45 Stat. 1057. The Act authorized the Secretary of the Interior to construct, operate, and maintain a dam and other works in order to control floods, improve navigation, regulate the river’s flow, store and distribute waters for reclamation and other beneficial uses, and generate electrical power. The projects authorized by the Act were the same as those provided for in the prior defeated measures, but in other significant respects the Act was strikingly different. The earlier bills •had offered no method whatever of apportioning the waiters among the States of the Lower Basin. The Act as finally passed did provide such a method, and, as we view it, the method chosen was a complete statutory apportionment intended to put an end to the long-standing dispute over Colorado River waters. To protect the Upper Basin against California should Arizona still refuse to ratify the Compact, § 4 (a) of the Act as finally passed provided that, if fewer than seven States ratified within six months, the Act should not take effect unless six States including California ratified and unless California, by its legislature, agreed “irrevocably and unconditionally . . . as an express covenant” to a limit on its annual consumption of Colorado River water of “four million four hundred thousand acre-feet of the waters apportioned to the lower basin States by paragraph (a) of Article III of the Colorado River compact, plus not more than one-half of any excess or surplus waters unapportioned by said compact.” Congress in the same section showed its continuing desire to have California, Arizona, and Nevada settle their own differences by authorizing them to make an agreement apportioning to Nevada 300,000 acre-feet, and to Arizona 2,800,000 acre-feet plus half of any surplus waters unap-portioned by the Compact. The permitted agreement also was to allow Arizona exclusive use of the Gila River, wholly free from any Mexican obligation, a. position Arizona had taken from the beginning. Sections-5 and 8 (b) of the Project Act made provisions for the sale of the stored waters. The Secretary of the Interior was authorized by § 5 “under such general regulations as he may prescribe, to contract for the storage of water in said reservoir and for the delivery thereof at such points on the river and on said canal as may be agreed upon, for irrigation and domestic uses . . . .” Section 5 required these contracts to be “for permanent service” and further provided, “No person shall have or be entitled to have the use for any purpose of the water stored as aforesaid except by contract made as herein stated.” Section 8 (b) provided that the Secretary’s contracts would be subject to any compact dividing the benefits of the water between Arizona, California, and Nevada, or any two of them, approved by Congress on or before January 1, 1929, but that any such compact approved after that date should be “subject to all contracts, if any, made by the Secretary of the Interior under section 5 hereof prior to the date of such approval and consent by Congress.”
  The Project Act became effective on June 25, 1929, by Presidential Proclamation, after six States, including California, had ratified the Colorado River Compact and the California legislature had accepted the limitation of 4,400,000 acre-feet as required by the Act. Neither the three States nor any two of them ever entered into any apportionment compact as authorized by §§ 4 (a) and 8 (b). After the construction of Boulder Dam the Secretary of the Interior, purporting to act under the authority of the Project Act, made contracts with various water users in California for 5,362,000 acre-feet, with Nevada for 300,000 acre-feet, and with Arizona for 2,800,000 acre-feet of water from that stored at Lake Mead.
  The Special Master appointed by this Court found that the Colorado River Compact, the law of prior appropriation, and the doctrine of equitable apportionment — by which doctrine' this Court in the absence of statute resolves interstate claims according to the equities — do not control the issues in this case. The Master concluded that, since the Lower Basin States had failed to make a corppact to allocate the waters among themselves as authorized by §§ 4 (a) and 8 (b), the Secretary’s contracts with the States had within the statutory scheme of §§ 4 (a), 5, and 8 (b) effected an apportionment of the waters of the mainstream which, according to the Master, were the only waters to be apportioned under the Act. The Master further held • that, in the event of a shortage of water making it impossible for the Secretary to supply all the water due California, Arizona, and Nevada under their contracts, the burden of the shortage must be borne by each State in proportion to her share of the first 7,500,000 acre-feet allocated to the Lower Basin, that is, — by California, — by Arizona, and by Nevada, without regard to the law of prior appropriation.
  Arizona, Nevada, and the United States support with. few exceptions the analysis, conclusions, and becommen-dations of the Special Master’s report. These parties agree that Congress did not leave division of the waters to an equitable apportionment by this Court but instead created a comprehensive statutory scheme for the allocation of mainstream waters. Arizona, however, believes that the allocation formula established by the Secretary’s contracts was in fact the formula required by the Act. The United States, along with California, thinks the Master should not have invalidated the provisions of the Arizona and Nevada water contracts requiring those States to deduct from their allocations any diversions of water above Lake Mead which reduce the flow into that lake.
  California is in basic disagreement with almost all of the Master’s Report. She argues that the Project Act, like the Colorado River Compact, deals with the entire Colorado River System, not just the mainstream. This would mean that diversions within Arizona and Nevada of tributary waters flowing in those States would be charged against their apportionments and that, because tributary water would be added to the mainstream water in computing the first 7,500,000 acre-feet available to the States, there would be a greater likelihood of a surplus, of which California gets one-half. The result of California’s argument would be much more water for California and much less for Arizona. California also argues that the Act neither allocates the Colorado River waters nor gives the Secretary authority to make an allocation. Rather she takes the position that the judicial’doctrine of equitable apportionment giving full interstate effect to the traditional western water law of prior appropriation should determine the rights of the parties to the water. Finally, California claims that in any event the Act does not control in time of shortage. Under such circumstances, she says, this Court should divide the waters according to the doctrine of equitable apportionment or the law of prior appropriation, either of which, she argues, should result in protecting her prior uses.
  Our jurisdiction to entertain this suit is not challenged and could not well be since Art. Ill, § 2, of the Constitution gives this Court original jurisdiction of actions in which States are parties. In exercising that jurisdiction, we are mindful of this Court’s often expressed preference that, where possible, States settle their controversies by “mutual accommodation and agreement.” Those cases and others make it clear, however, that this Court does have a serious responsibility to adjudicate cases where there are actual, existing controversies over how interstate streams should be apportioned among States. This case is the most recent phase of a continuing controversy over the water of the Colorado River, which the States despite repeated efforts have been unable to settle. Resolution of this dispute’requires a determination of what apportionment, if any, is made by the Project Act and what powers are conferred by the Act upon the Secretary of the Interior. Unless many of the issues presented here are adjudicated, the conflicting claims of the parties will continue, as they do now, to raise serious doubts as to the extent of each State’s right to appropriate water from the Colorado River System for existing or new uses. In this situation we should and do exercise our jurisdiction.
  I.
  Allocation of Water Among the States and Distribution to Users.
  iWe have concluded, for reasons to be stated, that Congress in passing the Project Act intended to and did create its own comprehensive scheme for. the apportionment among California, Arizona, and Nevada of the Lower Basin’s share of the mainstream waters of the Colorado River, leaving each State its tributaries. Congress decided that a fair division of the first 7,500,000 acre-feet of’ such mainstream waters would give 4,40.0,000 acre-feet to California, 2,800,000 to Arizona, and 300,000 to Nevada; Arizona and California would each get one-half of any surplus. Prior approval was therefore given in the Act for a tri-state compact to incorporate these terms. The States, subject to subsequent congressional approval, were also permitted to agree on a compact with different terms. Division of the water did not, however, depend on the States’ agreeing to a compact, for Congress gave the Secretary of the Interior adequate authority to accomplish the division. Congress did this by giving the Secretary power to make contracts for the delivery of water and by providing that no person could have water without a contract.
  A. Relevancy of Judicial Apportionment and Colorado River Compact. — We agree’ with the Master that apportionment of the Lower Basin waters of the Colorado River is- not controlled by the doctrine of equitable apportionment or by the Colorado River Compact. It is true that the Court has used the doctrine of equitable apportionment to decide river controversies between States. But in those cases Congress had not made any statutory apportionment. In this case, we have decided that Congress has provided its own method for allocating among the Lower Basin States the mainstream water to which they are entitled under the Compact. Where Congress has so exercised its constitutional power over waters, courts have no power to substitute their own notions of an “equitable apportionment” for the apportionment chosen by Congress. Nor does the Colorado River Compact control this case. Nothing in that Compact purports to divide water among the Lower Basin States nor in any way to affect or control any future apportionment among those States or any distribution of water within a State. That the Commissioners were able to accomplish even a division of water between the basins is due to what is generally known as the “Hoover Compromise.”
  “Participants [in the Compact negotiations] have stated that the negotiations would have broken up but for Mr. Hoover’s proposal: that the Commission limit its efforts to a division of water between the upper basin and the lower basin, leaving to each basin the future internal allocation of its share.”
  And in fact this is all the Compact did. However, the Project Act, by referring to the Compact in several places, does make the Compact relevant to a limited extent. To begin with, the Act explicitly approves the Compact and thereby fixes a division of the waters between the basins which must be respected. Further, in several places the Act refers to terms contained in the Compact. For example, § 12 of the Act adopts the Compact definition of “domestic,” and § 6 requires satisfaction of “present' perfected rights” as used in the Compact. Obviously, therefore, those particular terms, though originally formulated only for the Compact’s allocation of water between basins, are incorporated into the Act and are made applicable to the Project Act’s allocation among Lower Basin States. The Act also declares that' the Secretary of the Interior and the United States in the construction, operation, and maintenance of the dam and other works and in the making of contracts shall be subject to and controlled by the Colorado River Compact. These latter references to the Compact are quite different from the Act’s adoption of Compact terms. Such references, unlike the explicit adoption of terms, were, used only to show that the Act and its provisions were in no way to upset, alter, or affect the Compact’s congressionally approved division of water between the basins. They were not intended to make the Compact and its provisions control or affect the Act’s allocation among and distribution of water within the States of the Lower Basin. Therefore, we look to the Compact for terms specifically incorporated in the Act, and we would also look to it to resolve disputes between the Upper and Lower Basins, were any involved in this case. But no such questions are here. We must determine what apportionment and delivery scheme in the Lower Basin has been effected through the Secretary’s contracts. For that determination, we look to the Project Act alone.
  B. Mainstream Apportionment. — The congressional scheme of apportionment cannot be understood without knowing what water Congress wanted apportioned. Under California’s view, which we reject, the first 7,500,000 acre-feet of Lower Basin water, of which California has agreed to use only 4,400,000, is made up of both mainstream and tributary water, not just mainstream water. Under the view of Arizona, Nevada, and the United States, with which we agree, the tributaries are not included in the waters to be divided but remain for the exclusive use of each State. Assuming 7,500,000 acre-feet or more in the mainstreám and 2,000,000 in the tributaries, California would get 1,000,000 acre-feet more if the tributaries are included and Arizona 1,000,000 less.
  California’s argument that the Project Act, like the Colorado River Compact, deals with the main river and all its tributaries rests on § 4 (a) of the Act, which limits California to 4,400,000 acre-feet “of the waters apportioned to the lower basin States by paragraph (a) of Article III of the Colorado River compact, plus not more than one-half of any excess or surplus waters unappor-tioned by said compact . . . .” And Article III (a), referred to by § 4 (a), apportioned in perpetuity to the Lower Basin the use of 7,500,000 acre-feet of water per annum “from the Colorado River System,” which was defined in the Compact as “that portion of the Colorado River and its tributaries within the United States of America.”
  Arizona argues that the Compact apportions between basins only the waters of the mainstream, not the mainstream and the tributaries. We need not reach that question, however, for we have concluded that whatever waters the Compact apportioned the Project Act itself déalt only with water of the mainstream. In the first place, the Act, in § 4 (a), states that the California limitation, which is in reality her share of the first 7,500,000 acre-feet of Lower Basin water, is on “water of and from the Colorado River,” not of and from the “Colorado River System.” But more importantly, the negotiations among the States and the congressional debates leading to the passage of the Project Act clearly show that the language used by Congress in the Act was meant to refer to mainstream waters only. Inclusion qf the tributaries in the Compact was natural in view of the upper States’ strong feeling that the Lower Basin tributaries should be made to share the burden of any obligation to deliver water to Mexico which a future treaty might impose.. But when it came to an apportionment among the Lower Basin States, the Gila, by far the most important Lower Basin tributary, would not logically be included, since Arizona alone of the States could effectively use that river. Therefore, with minor exceptions, the proposals and counterproposals over the years, culminating in the Project Act, consistently provided for division of the mainstream only, reserving the tributaries to each State’s exclusive use.
  The most important negotiations among the States, which in fact formed the basis of the debates leading to passage of the Act, took place in 1927 when the Governors of the seven basin States met at Denver in an effort to work out an allocation- of the Lower Basin waters acceptable to Arizona, California, and Nevada. Arizona and California made proposals, both of which suggested giving Nevada 300,000 acre-feet out of the mainstream of the Colorado River and reserving to each State the exclusive use of her own tributaries. Arizona proposed that all remaining mainstream water be divided equally between herself and California, which would, give each State 3,600,000 acre-feet out of the first 7,500,000 acre-feet of mainstream water. California rejected the proposed ' equal division of the water, suggesting figures that would result in her getting about 4,600,000 out of the 7,500,000. The Governors of the four Upper Basin States, trying to bring Arizona and California together, asked each State to reduce its demands and suggested this compromise: Nevada 300,000 acre-feet, Arizona 3,000,000,.and California 4,200,000. These allocations were to come only out of the mainstream, that is, as stated by the Governors, out of "the average annual delivery of water to be provided by the states of the upper division at Lees Ferry, under the terms of the Colorado River Compact.” The Governors’ suggestions, like those of the States, explicitly reserved to each State as against the other States the exclusive use of her own tributaries. Arizona agreed to the Governors’ proposal, but she wanted it made clear that her tributaries were to be exempted from any Mexican obligation. California rejected the whole proposal, insisting that she must have 4,600,000 acre-feet from the mainstream, or, as she put it, “from the waters to be provided by the States of the upper division at Lee Ferry under the Colorado River' compact.”' Neither in the States’ original offers, nor in the Governors’ suggestions, nor in the States’ responses was the “Colorado River System” — mainstream plus tributaries — ever used as the basis for Lower Basin allocations; rather, it was always mainstream water, or the water to be delivered by the upper States at Lee Ferry, that is to say, an annual average of 7,500,000 acre-feet of mainstream water.
  With the continued failure of Arizona and California to reach accord, there was mounting impetus for a congressional solution. A Swing-Johnson bill containing no limitation on California’s uses finally passed the House in 1928 over objections by Representatives from Arizona and Utah. .When the bill reached the Senate, it was amended in committee to provide that the Secretary in his water delivery contracts must limit California to 4,600,000 ■ acre-feet “of the water allocated to the lower basin by the Colorado River compact . . . and one-half of the unallocated, excess, and/or surplus water . . . .” On the floor, Senator Phipps of Colorado proposed an amendment which would allow the Act to go into effect without any limitation on California if seven States ratified the Compact; if only six States ratified and if the California Legislature accepted the limitation,- the Act could still become effective. Arizona’s Senator Hayden had already proposed an amendment reducing California’s share to 4,200,000 acre-feet (the Governors’ proposal), plus half of the surplus, leaving Arizona exclusive use of the Gila free from any Mexican obligation, but this the Senate rejected. Senator Bratton of New Mexico, noting that only 400,000 acre-feet kept Arizona and California apart, immediately suggested an amendment by which they would split the difference, California getting 4,400,000 acre-feet “of the waters apportioned to the lower basin States by the Colorado River compact,” plus half of the surplus. It was this Bratton amendment that became part of the Act as passed, which had been amended on the floor so that the limitation referred to waters apportioned to the Lower Basin “by paragraph (a) of Article III of the Colorado River compact,” instead of waters apportioned “by the Colorado River compact.”
  Statements made throughout the debates make it quite clear ..that Congress intended the 7,500,000 acre-feet it was allocating, and out of which California was limited to 4,400,000, to be mainstream water only. In the first place, the basin Senators expressly acknowledged as the starting point for their debate the Denver Governors’ proposal that specific allocations be made to Arizona, California, and Nevada from the mainstream, leaving the tributaries to the States! For example, Senator Johnson, leading spokesman for California, and Senator Hayden, leading spokesman for Arizona, agreed that the Governors’ recommendations could be used as “a basis for discussion.” Hayden went on to observe that the Committee amendment would give California the same 4,600,000 acre-feet she had sought at Denver. Later, Nevada’s Senator Pittman stated that the committee “put the amount in there that California demanded before the four governors at Denver,” and said that the Bratton amendment would split the 400,000 acre-feet separating the Governors’ figure and the Committee’s figure. All the leaders in the debate — Johnson, Bratton, King, Hayden, Phipps, and Pittman — expressed a common understanding that • the key issue separating Arizona and California was the difference of 400,000 acre-feet, precisely the same 400,000 acre-feet of mainstream water that had separated the States at Denver. Were we to sustain California’s argument here that tributaries must be included, California would actually get more than she was willing to settle for at Denver.
  That the apportionment was from the mainstream only is also strongly indicated by an analysis of the second paragraph of § 4 (a) of the .Act. There Congress authorized Arizona, Nevada, and California to make a compact allocating to Nevada 300,00.0 acre-feet and .to Arizona 2,800,000 plus one-half of the surplus, which,' with California’s 4,400,000 and half of the surplus, would under California’s interpretation of the Act exhaust the Lower Basin waters, both mainstream and tributaries. But Utah and New Mexico, as Congress knew, had interests in Lower Basin tributaries which Congress surely would have protected in some way had it meant for the tributaries of those two States to be included in the water to be divided among Arizona, Nevada, and California. We cannot believe that Congress would have permitted three States to divide among themselves water belonging to five States. Nor can we believe that the representatives of Utah and New Mexico would have sat quietly by and acquiesced in a congressional attempt to include, their tributaries in waters given the other three States. ■
  Finally, in considering California’s claim to share in the tributaries of other States, it is important that from the beginning of the discussions and negotiations which led to the Project Act, Arizona consistently claimed that she must have sole use of the Gila, upon which her existing economy depended. Arizona’s claim was supported by the fact that only she and New Mexico could effectively use the Gila waters, which not only entered the Colorado River too close to Mexico to be of much use to any other State but also was reduced virtually to a trickle in the hot Arizona summers before it could reach the Colorado. In the debates the Senators consistehtly acknowledged that the tributaries — or at least the waters of the Gila, the only major Arizona tributary — were excluded from the allocation they were making. Senator Hayden, in response to questions by Senator Johnson, said that the California Senator was correct in stating that the Senate had seen fit to give Arizona 2,800,000 acre-feet in addition to all the water in the Gila. Senator Johnson had earlier stated, “[I]t is only the main stream, Senators will recall, that has been discussed,” and one of his arguments in favor of California’s receiving 4,600,000 acre-feet rather than 4,200,000 was that Arizona was going to keep all her tributaries in addition .to whatever portion of the •main river was allocated to her. Senator Johnson also argued that Arizona should bear more than half the Lower Basin’s Mexican burden because in addition to the 2,800,000 acre-feet allotted her by the Act she would get the Gila, which he erroneously estimated at 3,500,000 acre-feet. Senator Pittman, who had sat in on the Governors’ conference, likewise understood that the water was being allocated from “the main Colorado River.” And other interested Senators similarly distinguished between the mainstream and the tributaries. While the debates, extending over a long period of years, undoubtedly contain statements which support inferences in conflict with those we have drawn, we are persuaded by the legislative history as a whole that the Act was not intended to give California any claim to share in the tributary waters of the other Lower Basin States.
  C. The Project Act’s Apportionment and Distribution Scheme. — The legislative history, the language of the Act, and the scheme established by the Act for the storage and delivery of water convince us also that Congress intended to provide its own method for a complete apportionment of the mainstream water among Arizona, California, and Nevada.
  First, the legislative history. In hearings on the House bill that became the Project Act, Congressman Arentz of Nevada, apparently impatient with the delay of this much needed project, told the committee on January 6, 1928, that if the States could not themselves allocate the water, “there must be some power which will say to California ‘You can not take any more than this amount and the balance is allocated to the other States.’ ” Later, May 25, 1928, the House passed the bill, but it did not contain any allocation scheme. When the Senate took up that bill in December, pressure mounted swiftly for amendments that would provide a workable method for apportioning the waters among the Lower Basin States and distributing them to users in the States. The session convened on December 3, 1928, on the fifth the Senate took up the bill, nine days later the bill with significant amendments passed the Senate, four days after that the House concurred in the Senate’s action, and on the twenty-first the President signed the bill. When the bill first reached the Senate floor', it had a provision, added in committee, limiting California to 4,600,000 acre-feet-, and Senator Hayden on December 6 proposed reducing that share to 4,200,000. The next day, December 7, Mr. Pittman, senior Senator from Nevada, vigorously argued that Congress should settle the matter without delay. He said,
  “What is the difficulty? We have only minor questions involved here. There is practically nothing involved except a dispute between the States of Arizona and California with regard to the division of the increased water that will be impounded behind the proposed dam; that is all. ... Of the 7,500,000 acre-feet of water let down that river they have gotten together within 400,000 acre-feet. They have got to get together, and if they do not get together Congress should bring them together.”
  The day after that, December 8, New Mexico’s Senator Bratton suggested an amendment splitting the difference between the demands of Arizona and California by limiting California to 4,400,000 acre-feet. On the tenth, reflecting the prevailing sense of urgency for decisive action, Senator Bratton emphasized that this was not a dispute limited simply to two States:
  “The two States have exchanged views, they have negotiated, they have endeavored to reach an agreement, and until now have been unable to do so. This controversy does not affect those two States alone. It affects other States in the Union and the Government as well.
  “Without undertaking to express, my views either way upon the subject, I do think that if the two States are unable to agree upon a figure then that we, as a disinterested and friendly agency, should pass a bill which, according to our combined judgment, will justly and equitably settle the controversy. I suggested 4,400,000 acre-feet with that in view. I still hold to the belief that somewhere between the two figures we must fix the amount, and that this difference of 400,000 acre-feet should not be allowed to bar and preclude the passage of this important measure dealing with the enormous quantity of 15,000,000 acre-feet of water and involving seven States as Well as the Government.”
  The very next day, December 11, this crucial amendment was adopted, and on the twelfth Senator Hayden pointed out that the bill settled the dispute over Lower Basin waters by giving 4,400,000 acre-feet to California and 2,800,000 to Arizona:
  “One [dispute] is how the seven and a half million acre-feet shall be divided in the lower basin. The Senate' has settled that by a vote — that California may have 4,400,000 acre-feet of that water. It follows logically that if that demand is to be conceded, as everybody agrees, the remainder is 2,800,000 acre-feet for Arizona. That settles that part of the controversy.”
  On the same day, Senator • Pittman, intimately familiar with the whole water problem, summed up the feeling of the Senate that the bill fixed a limit on California and “practically allocated” to Arizona her share of the water:
  “The Senate has already determined upon the division of water between those States. How? It has determined how much water California may use, and the rest of it is subject to use by Nevada ánd Arizona. Nevada has already admitted that it can use only an insignificant quantity, 300,000 acre-feet. That leaves the rest of it to Arizona. As the bill now stands it is just as much divided as if they had mentioned Arizona and Nevada and the amounts they are to get ... .
  “As I understand this amendment, Arizona to-day has practically allocated to it 2,800,000 acre-feet of water in the main Colorado Rivér.”
  The Senator went on to explain why the Senate had found it necessary to set up its own plan for allocating the water:
  “Why do we-not leave it to California to say how much water she shall take out of the river or leave it to Arizona to say how much water she shall take out of the river? It is because it happens to become a duty of the United States Senate to settle this matter, and that is the reason.”
  Not only do the closing days of the debate show that Congress intended an apportionment among the States but also provisions of the Act create machinery plainly adequate to accomplish this purpose, whatever contingencies might occur. As one alternative of the congressional scheme, § 4 (a) of the Act invited Arizona, California, and Nevada to adopt a compact dividing the waters along the identical lines that had formed the basis for the congressional discussions of the Act: 4,400,000 acre-feet to California, 300,000 to Nevada, and 2,800,000 to Arizona. Section 8 (b) gave the States power to agree upon some other division, which would have to be approved by Congress. Congress made sure, however, that if the States did not agree on any compact the objects of the Act would be carried out, for the Secretary would then proceed, by making contracts, to apportion water among the States and to allocate the water among users within each State.
  In the first section of the Act, the Secretary was authorized to “construct, operate, and maintain a dam and incidental works . . . adequate to create a storage reservoir of a capacity of not less than twenty million acre-feet of water . . .” for the stated purpose of “controlling the floods, improving navigation and regulating the flow of the Colorado River, providing for storage and for the delivery of the stored waters thereof for reclamation of public lands and other beneficial uses . . . ,” and generating electrical power. The whole point of the Act was to replace the erratic, undependable, often destructive natural flow of the Colorado with the regular, dependable release of waters conserved and stored by the project. Having' undertaken this beneficial project, Congress, in several provisions of the Act, made it clear that no one should use mainstream waters save in strict compliance with the scheme set up by the Act. Section 5 authorized the Secretary “under such general regulations as he may prescribe, to contract for the storage of water in said reservoir and for the delivery thereof at such points on the river ... as may be agreed upon, for irrigation and domestic uses . '. . .” To emphasize that water could be obtained from the Secretary alone, § 5 further declared, “No person shall have or be entitled to have the use for any purpose of the water stored as aforesaid except by contract made as herein stated.” The supremacy given the Secretary’s contracts was made clear in § 8 (b) of the Act, which provided that, while the Lower Basin States were free to negotiate a compact dividing the waters, such a compact if made and approved after January 1, 1929, was to be “subject to all contracts, if any, made by the Secretary of the Interior under section 5” before Congress approved the compact.
  These several provisions, even without legislative history, are persuasive that Congress intended the Secretary of the Interior, through his § 5 contracts, both to carry out the allocation of the waters of the main Colorado River among the Lower Basin States and to decide which users within each State would get water. The general authority to make contracts normally includes the power to choose with whom and upon what terms the contracts will be made. When Congress in an Act grants authority to contract, that authority is no less than the general authority, unless Congress has placed some limit on it. In this respect it is of interest that in an earlier version the bill did limit the Secretary’s contract power by making the contracts “subject to rights of prior appropriators.” But that restriction, which preserved the law of prior appropriation, did not survive. It was stricken from the bill when the requirement that every water user have a contract was added to § 5. Significantly, no phrase or provision indicating that the Sécre-tary’s contract power was to be controlled by the law of prior appropriation was substituted either then or at any other time before passage of the Act, and we are persuaded that had Congress intended so to fetter the Secretary’s discretion, it would have done so in clear and unequivocal terms, as it did in recognizing “present perfected rights” in § 6.
  That the bill was giving the Secretary sufficient power to carry out an allocation of the waters among the States and among the users within each State without regard to the law of prior- appropriation was brought out in a colloquy between Montana’s Senator Walsh and California’s Senator Johnson, whose State had at least as much reason as any other State to bind the Secretary by state laws. Senator Walsh, who was thoroughly versed in western water law and also had previously argued before this Court in a leading case involving the doctrine of prior appropriation, made cléar what would follow from the Government’s impounding of the Colorado River waters when he said, “I always understood that the interest that stores the water has a right superior to prior appropriations that do not store.” He sought Senator Johnson’s views on what rights the City of Los Angeles, which had filed claims to large quantities of Colorado River water, would have after the Government had built the dam and impounded the waters. In reply to Senator Walsh’s specific question whether the Government might “dispose of the stored water as it sees fit,” Senator Johnson said, “Yes; under the terms of this bill.” Senator Johnson added that “everything in this scheme, plan, or design” was “dependent upon the Secretary of the Interior contracting with those who desire to obtain the benefit of the construction . . . .” He admitted that it was possible that the Secretary could “utterly ignore” Los Angeles’ appropriations.
  In this same discussion, Senator Hayden emphasized the Secretary’s power to allocate the water by making contracts with users- After Senator Walsh said that he understood Senator Johnson to be arguing that the Secretary must satisfy Los Angeles’ appropriations, Senator Hayden corrected him, pointing out that Senator Johnson had qualified his statement by saying that “after all, the Secretary of the Interior could allow the city of Los Angeles to have such quantity of water as might be determined by contract.” Senator Hayden went on to say that, where domestic and irrigation needs conflicted, “the Secretary of the Interior will naturally decide as between applicants, one who desires to use the water for potable purposes in the city and another who desires to use it for irrigation, if there is not enough water to go around, that the city shall have the preference.” It is also significant that two vigorous opponents of the bill, Arizona’s Representative Douglas and Utah’s Representative Col-ton, criticized the bill because it gave the Secretary of the Interior “absolute control” over the disposition of the stored waters.
  The argument that Congress would not have delegated to the Secretary so much power to apportion and distribute the water overlooks the ways in which his power is limited and channeled by standards in the Project Act. In particular, the Secretary is bound to observe the Act’s limitation of 4,400,000 acre-feet on California’s consumptive uses out of the first 7,500,000 acre-feet of mainstream water. This necessarily leaves the remaining 3,100,000 acre-feet for the use of Arizona and Nevada, since they are the only other States with access to the main Colorado River. Nevada consistently took the position, accepted by the other States throughout the debates, that her conceivable needs would not exceed 300,000 acre-feet, which, of course, left 2,800,000 acre-feet for Arizona’s use. Moreover, Congress indicated that it thought this a proper division of the waters when in the second paragraph of § 4 (a) it gave advance consent to a tri-state compact adopting such division. While no such compact was ever entered into, the Secretary by his contracts has apportioned the water in the approved amounts and thereby followed the guidelines set down by Congress'. And, as the Master pointed out, Congress set up other standards and placed other significant limitations upon the Secretary’s power to distribute the stored waters. 'It specifically set out in order the purposes for which the Secretary must use the dam and the reservoir:
  “First, for river regulation, improvement of navigation, and flood control; second, for irrigation and domestic uses and satisfaction of present perfected rights in pursuance of Article VIII of said Colorado River compact; and third, for power.” § 6.
  The Act further requires the Secretary to make revenue provisions in his contracts adequate to ensure the recovery. of the expenses of construction, operation, and maintenance of the dam and other works within 50 years after their construction. §4(b). The Secretary is directed to make water contracts for irrigation and domestic uses only for “permanent service.” § 5. He and his permittees, licensees, and contractees are subject to the Colorado River Compact, § 8 (a), and therefore can do nothing to upset or encroach upon the Compact’s allocation of Colorado River water between the Upper and Lower Basins. In the construction, operation,- and management of the work's, the Secretary is subject to the provisions of the reclamation law, except as the Act otherwise provides. § 14. One of the most significant limitations in the Act is- that the Secretary is required to satisfy present perfected rights, a matter of intense importance to those who had reduced their water rights tq actual beneficial use at the time the Act becamé effective. § 6. Arid, of course, all of the powers granted by'the Act are exercised by the Secretary and his well-established executive department, responsible to Congress and the President and subject to judicial review.
  Notwithstanding the Government’s construction, ownership, operation, and maintenance of the vast Colorado River works that conserve and store the river’s waters and the broad power given by Congress to the Secretary of the Interior to make contracts for the distribution of the water, it is argued that Congress in §§14 and 18 of the Act took away practically all the Secretary’s power by permitting the States to determine with whom and on what terms the Secretary would make water contracts. Section 18 states:
  “Nothing herein shall be construed as interfering with such rights as the. States now have either to the waters within their borders or to adopt such policies and enact such laws as they may deem necessary with respect to the appropriation, control, and use of waters within their borders . . . .”
  Section 14 provides that the reclamation law, to which the Act is made a supplement, shall govern the management of the works except as otherwise provided, and § 8 of the Reclamation Act, much like § 18 of the Project Act, provides that it is not to be construed as affecting or interfering with state laws “relating to the control, appropriation, use, or distribution of water used in irrigation . . . .” In our view, nothing in any of these provisions affects our decision, stated earlier, that it is the Act and the Secretary’s contracts, not the law of prior appropriation, that control the apportionment of water among the States. Moreover, contrary to the Master’s conclusion, we hold that the Secretary in choosing between users within each State and in settling the terms of his contracts is not bound by these sections to follow state law.
  The argument that § 8 of the Reclamation Act requires the United States in the delivery of water to follow priorities laid down by state law has already been disposed of by this Court in Ivanhoe Irr. Dist. v. McCracken, 357 U. S. 275 (1958), and reaffirmed in City of Fresno v. California, 372 U. S. 627 (1963). In Ivanhoe we held that, even though § 8 of the Reclamation Act preserved state law, that general provision could not override a specific provision of the same Act prohibiting a single landowner from getting water for more than 160 acres. We said:
  “As we read § 8, it merely requires the United States to comply with state law when, in the construction and operation of a reclamation project, it becomes necessary for it to acquire water rights or vested interests therein. But the-acquisition of water rights must not be confused with the operation of federal projects. As the Court said in Nebraska v. Wyoming, supra, at 615: We do not suggest that where Congress has provided a system of regulation for federal projects it must give way before an inconsistent state system.’. . . We read nothing in § 8 that compels the United States to deliver water on conditions imposed by the State.” Id.; at 291-292.
  Since § 8 of the Reclamation Act did not subject the Secretary to state law in disposing of water in that case, we cannot, consistently with Ivanhoe, hold that the Secretary must be bound by state law in disposing of water under the Project Act. .
  Nor does § 18 of the Project Act require the Secretary to contract according to state law. That Act was passed in the exercise of congressional power to control navigable water for purposes of flood control, navigation, power generation, and other objects, and is equally sustained by the power of Congress to promote the general welfare through projects for reclamation, irrigation, or other internal improvements. Section- 18 merely preserves such rights as the States “now” have, that is, such rights as they had at the time the Act was passed. While the States were generally free to exercise some jurisdiction over these waters before the Act was passed, this right was subject to the Federal Government’s right to regulate and develop the river. Where the Government, as here, has exercised this power and undertaken a comprehensive project for the improvement of a great river and for the orderly and beneficial distribution of water, there is no room for inconsistent state laws. As in Ivanhoe, where the general provision preserving state law was held not to override a specific provision stating the terms for disposition of the water, here we hold that the general saving language of § 18 cannot bind the Secretary by state law and thereby nullify the contract power expressly conferred upon him by § 5. Section 18 plainly allows the States to do things not inconsistent with the Project Act or with federal control of the river, for example, regulation of the use of tributary water and protection of present perfected rights. What other things the States are free to do can be decided when the occasion arises. ■ But where the Secretary’s contracts, as here, carry out a. congressional plan for the complete distribution of waters to users, state law has no place.
  Before the Project Act was passed, the waters of the Colorado River, though numbered' by the millions of acre-feet, flowed too haltingly or too freely, resulting in droughts and floods. The problems caused by thpse conditions proved too- immense and the solutions too costly for any one State or all the States together. In addition, the States, despite repeated efforts at a settlement, were unable to agree on how much water each State should get. With the health and growth of the Lower Basin at stake, Congress responded to the pleas of the States to come to their aid.., The result ■ was ■ the Project Act and the harnessing of the bountiful waters of the Colorado to sustain growing cities, to support expanding industries, and to transform dry and barren deserts into lands that are livable and productive.
  In undertaking this ambitious and expensive project for the welfare of the people of the Lower Basin States and of the Nation, the United States assumed the responsibility for the construction, operation, and supervision of Boulder Dam and a great complex of other dams and works. Behind the dam were stored virtually all the waters of the main river, thus impounding not only the natural flow but also the great quantities of water previously allowed to run waste or to wreak destruction. The impounding of these waters, along with their regulated and systematic release to those with contracts, has promoted the spectacular development of the Lower Basin. Today, the United States operates a whole network of useful projects up and down the river, including the Hoover Dam, Davis Dam, Parker Dam, Headgate-' Rock Dam, Palo Verde Dam, Imperial Dam, Laguna Dam, Morelos Dam, and the All-American Canal System, and many lesser works. It was only natural that the United States, which was to make the benefits available and which had accepted the responsibility for the project’s operation, would want to make certain that the waters were effectively used. All this' vast,, interlocking machinery — a dozen major works delivering water according to congressionally fixed priorities for home, agricultural, and industrial uses to people spread over thousands of square miles — could function efficiently only under unitary management, able to formulate and supervise a coordinated plan that could take account of the diverse, often conflicting interests of the people and communities of the Lower Basin States. Recognizing this, Congress put the Secretary of the Interior in charge of these works and entrusted him with sufficient power, principally the § 5 contract power, to direct, manage, and coordinate their operation. Subjecting the Secretary to the varying, possibly inconsistent, commands of the different state legislatures could frustrate efficient operation of the project and thwart full realization of the benefits Congress intended this national project to bestow. We are satisfied that the Secretary's power must be construed to permit him, within the boundaries set down in the Act, to allocate and distribute the waters of the mainstream of the Colorado River.
  II.
  Provisions in the Secretary's Contracts.
  A. Diversions above Lake Mead. — The Secretary’s contracts with Arizona and Nevada provide that any waters diverted by those States out of the mainstream or the tributaries above Lake Mead must be charged to their respective Lower Basin apportionments. The Master, however, took the view that the apportionment was to be made out of the waters actually stored at Lake Mead or flowing in the mainstream below Lake Mead. He therefore held that the Secretary was without power to charge Arizona and Nevada for diversions made by them from the 275-mile stretch of river between Lee Ferry and Lake Mead or from the tributaries above Lake Mead. This conclusion was based on the Master’s reasoning that the Secretary was given physical control over the waters stored in Lake Mead and not over waters before they reached the lake.
  We hold that the Master was correct in deciding that the Secretary cannot reduce water deliveries to Arizona and Nevada by the amount of their uses from tributaries above Lake'Mead, for, as we have held, Congress in the Project Act intended to apportion only the mainstream, leaving to each State its own tributaries. We disagree, however, with the Master’s holding that the Secretary is powerless to charge States for diversions from the mainstream above Lake Mead. What Congress was doing in the Project Act was providing for an apportionment among the Lower Basin States of the water allocated to that basin by the Colorado River Compact. The Lower Basin, with which Congress was dealing, begins at Lee Ferry, and it was all the water in the mainstream below Lee Ferry that Congress intended to divide among the States. Were we to refuse the Secretary the power to charge States for diversions from the mainstream between Lee Ferry and the damsite, we would allow individual States, by making diversions that- deplete the Lower Basin’s allocation, to upset the whole plan of apportionment arrived at by Congress to settle the long-standing dispute in the Lower Basin.' That the congressional apportionment scheme would.be upset can easily be demonstrated. • California, for example, has been allotted 4,400,000 acre-feet of mainstream water. If Arizona and Nevada can, without being charged for it, divert water from the river above Lake Mead, then California could not get the share Congress intended her to have.
  B. Nevada Contract. — Nevada has excepted to her inclusion in Paragraph II (B)(7) of the Master’s recommended decree, which provides that “mainstream water ¡shall be delivered to users in Arizona, California and Nevada only if contracts have been made by the Secretary of the Interior, pursuant to Section 5 of the Boulder Canyon Project Act, for delivery of such water.” While the . California contracts are directly with water users and the Arizona contract specifically contemplates further subcontracts with actual users, it is argued that the Nevada contract, made by the Secretary directly with the State of Nevada through her Colorado River Commission, should be construed as a contract to deliver water to the State without the necessity of subcontracts by the Secretary directly with Nevada water users. The United States disagrees, contending that properly construed the Nevada contract, like the Secretary’s general contract with Arizona, does not exhaust the Secretary’s power to require Nevada water users other than the State to make further contracts. To construe the Nevada contract otherwise, the 1 Government suggests, would bring it in conflict with the provision of § 5 of the Project Act that f‘No person shall have or be entitled to have the use for any purpose of the water stored as aforesaid except by contract [with the Secretary] made, as herein stated.” Acceptance of Nevada’s contention here would not only undermine this plain congressional requirement that water users have contracts with .the Secretary but would likewise transfer from the Secretary to Nevada a large part, if not all, of the Secretary’s power to determine with whom he will contract and on what' terms. We have already held that the contractual power granted the Secretary, cannot be diluted in this manner. We therefore reject Nevada’s contention.
  III.
  Apportionment and Contracts in Time . of Shortage.
  We have agreed with the Master that the Secretary’s contracts with Arizona for 2,800,000 acre-feet of water and with Nevada for 300,000, together with the limitation of California to 4,400,000 acre-feet, effect a valid apportionment of the first 7,500,000 acre-feet of mainstream water in the Lower Basin. There remains the question of what shall be done in time of shortage. The Master, while declining to make any findings as to .what future supply might be expected, nevertheless decided that the Project Act and the Secretary’s contracts require the Secretary in case of shortage to divide the. burden among the.three States in this proportion: California ; Arizona Nevada ■ While pro rata sharing of water shortages'seems equitable on its face, more considered judgment may demonstrate quite the contrary. Certainly we should not bind the Secretary to this formula. We have held that the Secretary is vested with considerable control over the apportionment of Colorado River waters. And neither the Project Act nor the water contracts require the use of any particular formula for apportioning shortages. While the Secretary must follow the standards set out in the Act, he nevertheless is free to choose among the recognized methods of apportionment or to devise reasonable methods of his own. This choice, as we see it, is primarily his, not the Master’s or even ours. And the Secretary may or may not conclude that a pro rata division is the best solution.
  It must be remembered that the Secretary’s decision may have an effect not only on. irrigation uses but also on other important functions for which Congress brought this great project into being — flood control, improvement of navigation, regulation of flow, and generation and distribution of electric power. Requiring the Secretary to prorate shortages would strip him of the very power of choice which we think Congress, for reasons satisfactory to it, vested in him and which we should riot impair or take away from him. For the same reasons we cannot accept California’s contention that in case of shortage each State’s share of water should be determined by the judicial doctrine of equitable apportionment or by the law of prior appropriation. These principles, while they may provide some guidance, are not binding upon the Secretary where, as here, Congress, with full power to do so, has provided that the waters of a navigable stream shall be harnessed, conserved, stored, and distributed through a government agency under a statutory scheme.
  None of this is to say that in case of shortage, the Secretary cannot adopt a method of proration or that he may not lay stress upon priority of use, local laws and customs, or any other factors that might be helpful in reaching an informed judgment in harmony with the Act, the best interests of the Basin States, and the weAare of the Nation. It will be time enough for the courts to intervene when and if the Secretary, in making appor-tionments or contracts, deviates from the standards Congress has set for him to follow, including his obligation to respect “present perfected rights” as of the date the Act was passed. At this time the Secretary has made no decision at all based on an actual or anticipated shortage of water, and so there is no action of his in this respect for us to review. Finally, as the Master pointed out, Congress still has broad powers over this navigable international stream. Congress, can undoubtedly reduce or enlarge the Secretary's power if it wishes. Unless and until it does, we leave in the hands of the Secretary, where Congress placed it, full power to control, manage, and operate the Government's Colorado River works and to make contracts for the sale and delivery of water on such terms as are not prohibited by the Project Act.
  IV.
  Arizona-New Mexico Gila Controversy."
  Arizona and New Mexico presented the Master with conflicting claims to water in the Gila River, the tributary that rises in New Mexico and flows through Arizona. Having determined that'tributaries are not within the regulatory provisions of the Project Act the Master held that this interstate dispute should be decided under the principles of equitable apportionment. After hearing evidence on this issue, the Master accepted a compromise settlement agreed upon by these States and incorporated that settlement in his findings and conclusions, and in Part IV (A) (B) (C) (D) of his recommended decree. No exceptions have been filed to these recommendations by any of the parties and they are accordingly accepted by us. Except for those discussed in Part V, we are not required to decide any other disputes between tributary . users or between mainstream and tributary users.
  V.
  Claims of the United States.
  In these proceedings, the United States has asserted claims to waters in the main river and in some of the tributaries for use on Indian Reservations, National Forests, Recreational and Wildlife Areas and other government lands and works. While the Master passed upon some of these claims, he declined to reach others, particularly those relating to tributaries. We approve his decision as to which claims required adjudication, and likewise we approve the decree he recommended for the government claims he did decide. We shall discuss only the ■claims of the United States on behalf of the Indian Reservations.
  The Government, on behalf of five Indian Reservations in Arizona, California, and Nevada, asserted rights to water in the mainstream of the Colorado River. The Colorado River Reservation, located partly in Arizona and partly in California, is the largest. It was originally created by an Act of Congress in 1865, but its area was later increased by Executive Order. Other-reservations were created by Executive Orders and amendments to them, ranging in dates from 1870 to 1907. The Master found both as a matter of fact and law that when the United States created these reservations or added to them, it reserved not only land but also the use of enough water from the Colorado to irrigate the irrigable portions of the reserved lands.. The aggregate quantity of water which the Máster held was reserved for all the reservations is about 1,00(3,000 acre-feet, to be used on around 135,000 irrigable acres of land. Here, as before the Master, Arizona argues that the United States had no power to make a reservation of navigable waters after Arizona became a State;; that navigable waters could not be reserved by Executive Orders; that the United States did not intend to reserve water for the Indian Reservations; that the amount of water reserved should be measured by the reasonably foreseeable needs of the Indians living on the reservation rather than by the numbér of irrigable acres; and, finally, that the judicial doctrine of equitable apportionment should be used to divide the water between the Indians and the other people in the State of Arizona.
  The last argument is easily answered. The doctrine of equitable apportionment is a method of resolving water disputes between States. It was created by this Court in the exercise of its original jurisdiction over controversies in which States are parties. An Indian Reservation is not a State. And while Congress has sometimes left Indian Reservations considerable power to manage their own affairs, we are not convinced by Arizona’s argument that each reservation is so much like a State that its rights to water should be determined by the doctrine of equitable apportionment. Moreover, even were we to treat an Indian Reservation like a State, equitable apportionment would still not control since, under our view, the Indian claims here are governed by the statutes and Executive Orders creating the reservations.
  Arizona’s contention that the Federal Government had no power, after Arizona became a State, to reserve waters for the use and benefit of federally reserved lands rests largely upon statements in Pollard’s Lessee v. Hagan, 3 How. 212 (1845), and Shively v. Bowlby, 152 U. S. 1 (1894). Those cases and others that followed them gave rise to the doctrine that lands underlying navigable • waters within territory acquired by the Government are held in trust for future States and that title to such lands is automatically vested in the States upon admission to the Union. But those cases involved only the shores of and lands beneath navigable waters. They do not determine the problem before us and cannot be accepted as limiting the broad powers of the United States to regulate navigable waters under the Commerce Clause and to regulate government lands under Art. IV, § 3, of the Constitution. We have no doubt about the power of the United States under these clauses to reserve water rights for its reservations and its property.
  Arizona also argues that, in any event, water rights cannot be reserved by Executive Order. Some of the reservations of Indian lands here involved were made almost 100 years ago, and all of them were made over 45 years ago. In our view, these reservations, like those created directly by Congress, were not limited to land, but included waters as well. Congress and the Executive have ever since recognized these as Indian Reservations. Numerous appropriations, including appropriations for irrigation projects, have been made by Congress. They have been uniformly and universally treated as reservations by map makers, surveyors, and the public. We can give but short shrift at this late date to the argument that the reservations either of land or water are invalid because they were originally set apart by the Executive.
  Arizona also challenges the Master’s holding as to the Indian Reservations on two other grounds: first, that there is a lack of evidence showing that the United States in establishing the reservations intended to reserve water for them; second, that even if water was meant to be reserved the Master has awarded too much water. We reject both of these contentions. Most of the land in these reservations is and alwáys has been arid. If the water necessary to sustain life is to be had, it must come from the Colorado River or its tributaries. It can be said without overstatement that when the Indians were put on these reservations they were not considered to be located in the most desirable area of the Nation. It is impossible to believe that when Congress created the great Colorado River Indian Reservation and when the Executive Department of this Nation created the other reservations they were unaware that most of the lands were of the desert kind — hot, scorching sands — and that water from the river would be essential to the life of the Indian people and to the animals they hunted and the crops they raised. In the debate leading to approval of the first congressional appropriation for irrigation of the Colorado River Indian Reservation, the delegate from the Territory of Arizona made this statement:
  “Irrigating canals are essential to the prosperity of these Indians. Without water there can be no production, no life; and all they ask of you is to give them a few agricultural implements to enable them to dig an irrigating canal by which their lands may be watered and their fields irrigated, so that they may enjoy the means of existence. You must provide these Indians with the means of subsistence or they will take by robbery from those who have. During the last year I have seen a number of these Indians starved to death for want of food.” Cong. Globe, 38th Cong., 2d Sess. 1321 (1865).
  The question of the Government’s implied reservation of water rights upon the creation of an Indian Reservation was before this Court in Winters v. United States, 207 U. S. 564, decided in 1908. Much the same argument made to us was made in Winters to persuade the Court to hold that Congress had created an Indian Reservation without intending to reserve waters' necessary to make the reservation livable. The Court rejected all of the arguments. As to whether water was intended to be reserved, the Court said, at p. 576:
  “The lands were arid and, without irrigation, were practically valueless. And yet, it is contended, the means of irrigation were deliberately given up by the Indians and deliberately accepted by the Government. The lands ceded were, it is true, also arid; and some argument may be urged, and is urged, that with their cession there was the cession of the waters, without which they would be valueless, and 'civilized communities could not be established thereon.’ And this, it is further contended, the Indians knew, and yet made no reservation of the waters. We realize that there is a conflict of implications, but that which makes for the retention of the waters is of greater force than that which makes for their cession.”
  The Court in Winters concluded that the. Government, when it created that Indian Reservation, intended to deal fairly" with the Indians by reserving for them the waters without which their lands would have been useless. Winters has been followed by this Court as recently as 1939 in United States v. Powers, 305 U. S. 527. We follow it now and agree that the United States did reserve the water rights for the Indians effectivé as of the time the Indian Reservations were created. This' means, as the Master held, that these water rights, having vested before the Act became effective on June 25, 1929, are “present perfected rights” and as such are entitled to priority under the Act.
  We also agree with the Master’s conclusion as to the quantity of water intended to be reserved. He found that the water was intended to satisfy the future as well as the present needs of the Indian Reservations and ruled that enough water was reserved to irrigate all the practicably irrigable acreage on the reservations. Arizona, on the other hand, contends that the quantity of water reserved should be measured by the Indians’ “reasonably foreseeable needs,” which, in fact, means by the number of Indians. How many Indians there will be and what their future' needs will be can only be guessed. We have concluded, as did the Master, that the only feasible and fair way by which reserved water for the reservations can be measured is irrigable acreage. The various acreages of irrigable land which the Master found to be on the different reservations we find to be reasonable.
  We disagree with the Master’s decisión to determine the disputed boundaries of the Colorado River Indian Reservation and . the Fort Mohave Indian Reservation. We hold that it is unnecessary to resolve those disputes here. Should a dispute over title arise because of some future refusal by the Secretary to deliver water to either area, the dispute can be settled at that time.
  The Master ruled that the principle underlying the reservation of water rights for Indian Reservations was equally applicable to other federal establishments such as National Recreation Areas and National Forests. We agree with the conclusions of the Master that the United States intended to reserve water sufficient for the future requirements of the Lake Mead National Recreation Area, the Havasu Lake National Wildlife Refuge, the Imperial National Wildlife Refuge and the Gila National Forest.
  We reject the claim of the United- States that- it is entitled to the use, without charge against its consumption, of any waters that would have been wasted but for salvage by the Government on its wildlife preserves. Whatever the intrinsic merits of this claim, it is inconsistent with the Act’s command that consumptive use shall be measured by diversions less returns to the river.
  Finally, we note our agreement with the Mastér that all uses of mainstream water within a State are to be charged against that State’s apportionment, which of course includes uses by the United States.
  VI.
  Decree.
  While we have in the main agreed with the Master, there are some places we have disagreed and some questions on which we have not ruled. Rather than adopt' the Master’s decree with amendments or append our own decree to this opinion, we will allow the parties, or any of them, if they wish, to submit before September 16, 1963, the form of decree to carry this opinion into effect, failing which the Court will prepare and enter an appropriate cjécree at the next Term of Court.
  It is so ordered.
  The Chief Justice took no part in the consideration or decision of this case.
  [For opinion of Mr. Justice Harlan, joined by Mr. Justice Douglas and Mr. Justice Stewart, see post, p. 603.]
  [For dissenting opinion of Mr. Justice Douglas, see post, p. 627.]
  “The judicial Power shall extend . , . to Controversies between two. or more States : ¡ . .
  “In all Cases ... in which a State shall be Party, the supreme Court shall have original Jurisdiction.” U. S. Const., Art. Ill, § 2. See also 28 V. S. C. § 1251 (a) (1).
  Three times previously Arizona has instituted actions in this Court concerning the Colorado River. Arizona v. California, 283 U. S. 423 (1931); Arizona v. California, 292 U. S. 341 (1934); Arizona v. California, 298 U. S. 558 (1936). See also United States v. Arizona, 295 U. S. 174 (1935).
  Palo Verde Irrigation District, Imperial Irrigation District, Coa-chella Valley County-'Water District, Metropolitan Water District of Southern California, City .of Los Angeles, City of.San Diego, and County of San Diego.
  344 U. S. 919 (1953) (intervention by United States); 347 U. S. 985 (1954) (intervention by Nevada); 350 U. S. 114 (1955) (joinder of Utah and New Mexico).
  The two orders are reported at 347 U. S. 986 (1954), and 350 U. S. 812 (1955).
  364 U. S. 940 (1961).
  Boulder Canyon Project Act, 45 Stat. 1057 (1928), 43 U. S. C. §§ 617-617t.
  “[The All-American Canal] will end an intolerable situation, under which the Imperial Valley now secures its sole water supply from a canal rumiing for many miles through Mexico . . . .” S. Rep. No. 592, 70th Cong., 1st Sess. 8 (1928).
  Department of the Interior, Report of the All-American. Canal Board (1919), 23-33. The three members of the Board were engineers with long experience in Western water problems.
  41 Stat. 600 (1920).
  S. Doc. No. 142, 67th Cong., 2d Sess. (1922)'.
  Id., at 1.
  The reasons given were:
  “1. The Colorado River is international.
  “2. The stream and many of its tributaries are interstate.
  “3. It is a navigable river.
  “4. Its waters may be made to serve large areas of public lands naturally desert in character.
  “5. Its problems are.of such magnitude as to be beyond the.reach of other than national solution.” Ibid.
  Id., at 21.
  This, law prevails exclusively in all the basin States .except California. See I Wiel, Water Rights in the Western States § 66 (3d ed., 1911); Hutchins, Selected Problems in the Law of Water Rights in the West 30-31 (1942) (U. S. Dept, of Agriculture Mise. Pub. No. 418). Even in California it is important. See 51 Cal. Jur. 2d Waters §§ 257-264(1959).
  Hinderlider v. La Plata River & Cherry Creek Ditch Co., 304 U. S. 92, 98 (1938); Arizona v. California, 283 U. S. 423, 459 (1931).
  The doctrine continues to be applied interstate. E. g., Nebraska v. Wyoming, 325 U. S. 589, 617-618 (1945).
  “Delph E. Carpenter, Colorado River Commissioner.for the State of Colorado, summarized the situation produced by that decision as follows:
  “ ‘The upper state has but. one alternative, that ,of using every means to retard development in the lower state until the uses within the upper state have reached their maximum. The states may avoid this unfortunate situation by determining their respective rights by interstate compact before further development in either state, thus permitting freedom of development in the lower state without injury to future growth in the upper.’
  “The final negotiation of the compact took place in the atmosphere produced by that decision.” H. R. Doc. No. 717, 80th Cong., 2d Sess.22 (1948).
  H. R. Rep. No. 191, 67th Cong., 1st Sess. (1921).,
  42 Stat. 171 (1921).
  The Compact can be found at 70 Cong. Rec. 324 (1928) , and U. S. Dept. of the Interior, Documents on the Use and Control of the Waters of Interstate and International Streams 39 (1956).
  H. R. Doc. No. 717, 80th Cong., 2d Sess. 22-(1948).
  An acre-foot of water is'enough .to' cover an acre of land with one . foot of water.
  “Beneficial consuriiptive' use” means consumptive use' measured by'diversions less return .flows, for a beneficial (nonwasteful) purpose.
  Arizona did ratify the Compact in 1944, after it had already become effective by six-state ratification as permitted by the Boulder Canyon Project Act.
  Hearings on H. R. 5773 before the House Committee on Irrigation and Reclamation, 70th Cong., 1st Sess. 402-405 (1928).
  Id., at 30-31. Arizona also objected to the provisions concerning electrical power.
  H. R. 11-449, 67th Cong., 2d Sess. (1922); -H. R. 2903, S. 727, 68th Cong., 1st Sess. (1923); H. R. 9826, S. 3331, 69th Cong., 1st' Sess. (1926).
  Another purpose of the Act was to approve the Colorado River • Compact, which had allocated the water between the two basins.
  The Upper Basin States feared that, if Arizona did not ratify the Compact, the division of water between the Upper and Lower Basins agreed on in the Compact would be nullified. The reasoning was that Arizona’s uses would not be charged against the Lower Basin’s apportionment and that California would therefore be free to exhaust that apportionment herself. Total Lower Basin uses would then be more than permitted .-in the Compact, leaving less-, water for the Upper Basin.
  46 Stat. 3000 (1929).
  California Limitation Act, Cal. Stat. 1929, c. 16, at 38.
  Colorado v. Kansas, 320 U. S. 383, 392 (1943); Nebraska v. Wyoming, 325 U. S. 589, 616 (1945).
  E. g., Kansas v. Colorado, 185 U. S. 125 (1902); New Jersey v. New York, 283 U. S. 336 (1931).
  E. g., Wyoming v. Colorado, 259 U. S. 419 (1922); Nebraska v. Wyoming, 325 U. S. 589 (1945).
  H. R. Doc. No. 717, 80th Cong., 2d Sess. 22 (1948).
  “ ‘Domestic’whenever employed in this Act shall include water uses defined as ‘domestic’'in said Colorado River compact.”
  The dam and reservoir shall be used, among other things, for “satisfaction of present perfected rights in pursuance of Article VIII of said Colorado River compact.”
  §§ 1, 8(a), 13 (b) and (c).
  Also, California would reducé Nevada’s share of the mainstream waters from 300,000 acre-feet to 120,500 acre-feet.
  Not only does the Gila enter the Colorado almost at the Mexican border, but also in dry seasons it virtually evaporates before reaching the Colorado.
  See 69 Cong. Rec. 9454 (1928).
  See 70 Cong. Rec. 172 (1928).
  Hearings on H. R. 5773, supra note 25, at 30-31.
  Id., at 402.
  H. R. 5773, 70th Cong., 1st Sess.; 69 Cong. Rec. 9989-9990 (1928).
  S. Rep. No. 592, 70th Cong., 1st Sess. 2 (1928).
  70 Cong. Rec. 324 (1928).
  Id., at 162.
  Id., at 384.
  Id., at 385.
  45 Stat. 1057 (1928). Arizona’s Senators Ashurst and Hayden voted against the bill, which did not exempt the Gila from the Mexican burden. 70 Cong. Rec. 603 (1928).
  70 Cong. Rec. 459 (1928). That this change was not intended .to cause the States to give up their tributaries may reasonably be inferred from the fact that the amendment was agreed to by Senator Hayden,'who was a constant opponent of including the tributaries.
  Id.,at 77.
  Ibid. Later, Senator Hayden said that his amendment incorporated the Governors’ proposal. Id., at 172-173.
  Id., at 386.
  Id., at 164 (King), 165 (Johnson, Bratton), 382 (Hayden, Phipps), 385 (Bratton), 386 (Pittman). Senator Hayden’s statement is representative: “I want to state to the"Senate that what I am trying to accomplish is to get a vote on the one particular question of whether the quantity of water which the State of California may divert from the Colorado River should be 4,200,000 acre-feet or 4,600,000 acre-feet.” Id., at 382.
  E. g., Report, Colorado River Commission of Arizona (1927), reprinted in Hearings on H. R. 5773, supra note 25, at 25-31; 69 Cong. Rec. 9454 (1928) (Arizona’s proposal at Denver).
  70 Cong. Rec. 467-468 (1928). See also id., at 463-464, 465.
  Id., at 237.
  Id., at 466-467.
  Id., at 469. See also id., at 232.
  See id., at 463 (Shortridge); id., at 465 (King).
  Hearings on H. R. 5773, supra note 25, at 50.
  69 Cong. Rec. 9990 (1928).
  70 Cong. Rec. 67 (1928).
  Id., at 603.
  Id., at 837-838.
  45 Stat. 1057.
  See S. Rep. No. 592, 70th Cong., 1st Sess. 2 (1928).
  70 Cong. Rec. 162 (1928).
  Id., at 232.
  Id., at 277, 385.
  Id., at 333.
  Id., at 387.
  Id., at 467. See also id., at 465.
  For example, Senator Pittman’s active role in resolving the whole Colorado River problem was acknowledged by Senator Hayden on the Senate floor:
  “When Congress assembled in December, 1927, no agreement had been made. The senior Senator from Nevada [Mr. Pittman], in continuation of the earnest efforts that he has made all these years to bring aboút a settlement of the controversy between the States with respect to the Colorado River, invited a number of us to conferences in his office and there >ve talked over the situation.” Id., at 172. •
  Id., at 468-469.
  Id., at 471. The Senator added, “We have already decided as to the division of the water, and we say that if the States wish they can enter into a subsidiary agreement confirming that.” Ibid.
  In the debates leading to the passage of the bill, Senator Walsh observed that “to contract means a liberty of contract” and asked if this did not mean that the Secretary could “give the water to them [appropriators] or withhold it from them as he sees fit,” to which Senator Johnson answered “certainly.” 70 Cong. Rec. 168 (1928).
  See Hearings on H. R. 6251 and' 9826 before the Committee on Irrigation and Reclamation, 69th Cong., 1st Sess. 12 (1926).
  See id., at 97, 115.
  Bean v. Morris, 221 U. S. 485 (1911). This case was relied on by Mr. Justice Van Devanter in Wyoming v. Colorado, 259 U. S. 419, 466 (1922).
  70 Cong. Rec. 168 (1928). Other statements by Senator John,son are less damaging to California’s claims. For example, the Senator at another point in the colloquy with Senator Walsh said that he doubted if the Secretary either would or could disregard Los Angeles and contract with someone having no appropriation. Ibid. It is likely, however, that Senator Johnson was talking about present perfected rights, as a few minutes before he had argued that Los Angeles had taken sufficient steps in perfecting its claims to make them protected. See id.; at"167. Present perfected rights, as we have observed in the text, are recognized by the Act. § 6.
  70 Cong. Rec. 169 (1928). At one point Senator Hayden seems to say-that the Secretary’s contracts are to be governed by state law: “The only thing required in this bill is contained in the amendment that I have offered, that there shall be apportioned to each State its share of the water.- Then, who shall obtain that water in relative order of priority may be determined by the State courts.” Ibid. But, in view of the Senator’s other statements in the same debate, this remark of a' man so knowledgeable in western water law makes sense only if one understands that the “order of priority” being talked about was the order of present perfected rights — rights which Senator Hayden recognized, see id., at 167, and which the Act preserves in § 6.
  69 Cong. Rec. 9623, 9648, 9649 (1928). We recognize, of course, that statements of opponents of a bill may not be authoritative, see Schwegmann Bros. v. Calvert Distillers Corp., 341 U. S. 384, 394-395 (1951), but they are nevertheless relevant and useful, especially where, as here, the proponents of the bill made no response to the opponents’ criticisms.
  See, e. g., Ickes v. Fox, 300 U. S. 82 (1937); cf. Best v. Humboldt Placer Mining Co. 371 U. S. 334 (1963); Boesche v. Udall, ante, p. 472.
  “Nothing in .... [this Act] shall be construed as affecting or intended to affect or to in any way interfere with the laws of any State or Territory relating to the control, appropriation, use, or distribution of water used in irrigation, or any vested right acquired thereunder, and the Secretary of the Interior, in carrying out the provisions of such sections, shall proceed in conformity with such laws, and nothing . . . [herein] shall in any way affect any right of any State or of the Federal Government or of any landowner, appropriator, or user of water in, to, or from any interstate stream or the waters thereof.” 43 U. S. C. § 383.
  Arizona v. California, 283 U. S. 423 (1931).
  United States v. Gerlach Live Stock Co., 339 U. S. 725, 738 (1950).
  First Iowa Hydro-Elec. Coop. v. Federal Power Comm’n, 328 U. S. 152, 171 (1946). See United States v. Chandler-Dunbar Water Power Co., 229 U. S. 53, 62-72 (1913); United States v. Willow River Power Co., 324 U. S. 499 (1945).
  See Arizona v. California, 283 U. S. 423 (1931); Nebraska v. Wyoming, 325 U. S. 589, 615 (1945); First Iowa Hydro-Elec. Coop. v. Federal Power Comm’n, 328 U. S. 152 (1946).
  Nebraska v. Wyoming, 325 U. S. 589 (1945), holds nothing to the contrary. There the Court found it unnecessary to decide what rights the United States had under federal law to the unappropriated water of the North Platte River, since the water rights on which the projects in that cáse rested had in fact been obtained in compliance with state law.
  See First Iowa Hydro-Elec. Coop. v. Federal Power Comm’n, 328 U. S. 152, 175-176 (1946), where this Court limited the effect of § 27 of the Federal Power Act, which expressly “saved” certain state laws, to vested property rights.
  By an Act of September 2, 1958, 72 Stat. 1726, the Secretary must supply water to Boulder City, Nevada. It follows from our conclusions as to the inapplicability of state law that, contrary to the blaster's conclusion, Boulder City’s priorities are not to be determined by Nevada law.
  The location of Hoover Dam is a result of engineering decisions. As Senator Pittman pointed out, “There is no place to impound the flood waters except at the lower end of the canyon.” 68 Cong. Rec. 4413 (1927).
  Proration of shortage is the method agreed upon' by the United States and Mexico to' adjust Mexico’s share of Colorado River water should there be insufficient water to supply each country’s apportionment.
  The Reservations were Chemehuevi, Coeopah, Yiyna, Colorado River and Fort Mohave.
  Act of March 3, 1865, 13 Stat. 541, 559.
  See Executive Orders of November 22, 1873, November 16, 1874, and May 15, 1876. See also Executive Order of November 22, 1915. These orders may- be found in 1 U. S. Dept. of the Interior, Executive Orders Relating to Indian Reservations-6-7 (1912); 2 id., at 5-6 (1922).
  Executive Orders of January 9, 1884 (Yuma), September 19, 1890 (Fort Mohave), February 2, 1911 (Fort Mohave), September 27, 1917 (Cocopah). For these orders, see 1 id., at 12-13, 63-64 (1912); 2 id., at 5 (1922). The Chemehuevi Reservation was established by the Secretary of the Interior on February 2, 1907, pending congressional approval
  See, e. g., United States v. California, 332 U. S. 19, 29-30. (1947); United States v. Holt State Bank, 270 U. S. 49, 54-55 (1926).
  See United States v. Midwest Oil Co., 236 U. S. 459, 469-475 (1915); Winters v. United States, 207 U. S. 564 (1908).
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