Hoover Dam, often called Boulder Dam, is located on the Colorado River at the southern tip of Nevada and the Arizona border. In the early 1900s, after many failed efforts to control the lower Colorado River with levees and irrigation canals, the U.S. Bureau of Reclamation decided the best solution for the arid Southwest would be to dam the river and create a year-round water supply. Surveyors investigated seventy sites along the entire river's course and settled on Nevada's Boulder and Black Canyons, both offering a potential reservoir of more than thirty million acre-feet.