The dam's name has changed over the years, but its modern name is Hoover, after the U.S. president in office during the initial construction. Hoover Dam, the height of a 60 story building, is the highest concrete dam in the U.S. and, at the time it was built, was the largest in the world. The dam regulates river flow, provides flood control, and stores water for portions of California, Nevada, Arizona, and Mexico. Because of the greater height between the upstream reservoir and the downstream outlet, it can produce some of the largest quantities of electricity in the U.S., generating about four billion kilowatt-hours of energy annually. Hoover Dam and Lake Mead are world-renowned tourist destinations, and Lake Mead National Recreation Area attracts more than seven million visitors per year.