History of the National Park Service and multi purpose river basin development programs like the Tennessee Valley Authority which began in the 1930s and spread to river valleys in all parts of the country after World War II. Lake Mead was the first National Recreation Area. The Boulder Canyon Project Act, passed in 1928, authorized the Bureau of Reclamation to construct Hoover Dam on the Colorado River. Work began in 1931 and the dam, highest in the Western Hemisphere, was completed in 1935. The next year, under provisions of an agreement with the Bureau of Reclamation, the National Park Service assumed responsibility for all recreational activities
Colorado River , poured into the sea. The United States Geological Survey (USGS) operates or has operated 46 stream gauges to measure the discharge of the Colorado River, ranging from the headwaters near Grand Lake to the Mexico–U.S. border. The tables at right list data associated with eight of these gauges. River flows as gauged at Lee's Ferry, Arizona, about halfway along the length of the Colorado and below Glen Canyon Dam, are used to determine water allocations in the Colorado River basin. The average discharge recorded there was approximately , per year, from 1921 to 2010. This figure has been heavily