Located between Nevada and Arizona, the Hoover Dam is a concrete arch-gravity dam situated in the Black Canyon of the Colorado River. The Hoover Dam marked the first ever dam constructed nearly entirely out of concrete. The dam is used to provide power to the state of Nevada, control floods, and impounds the water of Lake Mead, the largest reservoir in the United States. The Dam provides water to the states of Arizona, Nevada, and California. The site is very popular and is visited by over a million visitors each year.