opinion: Mr. Justice Douglas
  delivered the opinion of the Court.
  Petitioner brought this suit under § 17 of the Fair Labor Standards Act (52 Stat. 1060, as amended, 63 Stat. 910, 29 U. S. C. § 201 et seq.) to enjoin respondent from violating § 15 (a) (2) and § 15 (a) (5) of the Act. Those sections make unlawful violation of § 7 and § 11 (c) of the Act. Section 7 requires one and a half times the regular rate of pay for work in excess of 40 hours a week; and § 11 (c) requires the keeping of the records that are prescribed by regulations. 29 CFR, 1954 Cum. Supp., § 516.1 et seq. The contention is that respondent’s violations of § 7 and § 11 (c) relate to work performed in the construction of an earthwork embankment and concrete platform for the Algiers Lock in Orleans Parish, Louisiana, a unit in the Gulf Intracoastal Waterway, extending from Florida to the Mexican border. The Algiers Lock is designed to furnish better passage into and across the Mississippi than is provided by the present Harvey Lock and Canal.
  Respondent concedes that some of its employees on the Algiers Lock were employed for more than 40 hours per week without payment for overtime. Its defense is that its employees working on the Algiers Lock were not engaged in interstate commerce, and thus were not covered by the Act.
  The evidence at the trial was primarily directed to the question whether those working on the Algiers Lock were engaged in commerce within the meaning of § 7 of the Act. As already noted, the Algiers Lock will form part of the Gulf Intracoastal Waterway. It is designed to serve as an alternate route to the Harvey Lock and Canal. Relying on our decision in Raymond v. Chicago, M. & St. P. R. Co., 243 U. S. 43, the District Court held that respondent’s employees were not engaged in commerce and denied injunctive relief. 113 F. Supp. 235. The Court of Appeals for the Fifth Circuit affirmed per curiam. 214 F. 2d 132. To resolve an apparent conflict with Tobin v. Pennington-Winter Const. Co., 198 F. 2d 334, we granted certiorari. 348 U. S. 886.
  Section 7 of the Act makes the 40-hour week and the overtime provisions applicable to the Algiers Lock and Canal project if the respondent’s employees at work on it are "engaged in commerce.” It is argued that they are not engaged “in commerce,” since the Algiers Lock is new construction and therefore in the category of the new tunnel that was being constructed in Raymond v. Chicago, M. & St. P. R. Co., supra. In the latter case, the Court held that an employee at work on a new tunnel for an interstate carrier was not subject to the Federal Employers’ Liability Act, even though the tunnel, when completed, would be an interstate facility.
  We do not think that case should control this one. We are dealing with a different Act of another vintage — one that has been given a liberal construction from Kirschbaum Co. v. Walling, 316 U. S. 517, to Alstate Construction Co. v. Durkin, 345 U. S. 13. The question whether an employee is engaged “in commerce” within the meaning of the present Act is determined by practical considerations, not by technical conceptions. See Walling v. Jacksonville Paper Co., 317 U. S. 564, 570; Overstreet v. North Shore Corp., 318 U. S. 125, 128, 130. The test is whether the work is so directly and vitally related to the functioning of an instrumentality or facility of interstate commerce as to be, in practical effect, a part of it, rather than isolated, local activity. See McLeod v. Threlkeld, 319 U. S. 491, 497. Repair of facilities of interstate commerce is activity “in commerce” within the meaning of the Act, as we held in Fitzgerald Co. v. Pedersen, 324 U. S. 720. And we think the work of improving existing facilities of interstate commerce, involved in the present case, falls in the same category.
  The Gulf Intracoastal Waterway is an existing instrumentality of commerce. Without Algiers Lock, it has proved inadequate where it crosses the Mississippi. Harvey Lock cannot handle the traffic. Use of Harvey Lock entails travel through some five miles of the New Orleans harbor, already heavy with traffic. It is impractical to widen Harvey Lock because it is located in a highly developed industrial section of New Orleans. Algiers Lock is conceived as the practical alternative for relieving the congestion of the Waterway at this point. See S. Doc. No. 188, 78th Cong., 2d Sess., pp. 1-4. The work on Algiers Lock seems to us to have as intimate a relation to improvement of navigation on the Waterway as the dredging of Harvey Lock would have. It is part of the redesigning of an existing facility of interstate commerce. Those working on the Algiers Lock are therefore “engaged in commerce” within the meaning of § 7 of the Act.
  Reversed.
  Mr. Justice Harlan took no part in the consideration or decision of this case.
  The only question presented and argued here concerns § 7 of the Act.
  The construction work held in Murphey v. Reed, 335 U. S. 865, not to be under the Act was the building of a Navy base, not the improvement of a facility or instrumentality of interstate commerce.