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 affected by upstream diversions and reservoir evaporation, especially after the completion of the Colorado River Storage Project in the 1970s. Prior to the completion of Glen Canyon Dam in 1964, the average discharge recorded between 1912 and 1962 was , per year. The drainage basin or watershed of the Colorado River encompasses of southwestern North America, making it the seventh largest on the continent. About , or 97 percent of the watershed, is in the United States. The river and its tributaries drain most of western Colorado and New Mexico, southwestern Wyoming, eastern and southern Utah, southeastern Nevada and California,