Which river is dammed by the Hoover Dam?

Hoover Dam, originally known as Boulder Dam from 1933 to 1947, when it was officially renamed Hoover Dam by a joint resolution of Congress, is a concrete arch-gravity dam in the Black Canyon of the Colorado River. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. The dam was named after President Herbert Hoover.

As the technology of electric power transmission improved, the Lower Colorado River was considered for its hydroelectric-power potential. In 1902, the Edison Electric Company of Los Angeles surveyed the river in the hope of building a 40-foot (12 m) rock dam which could generate 10,000 horsepower (7,500 kW). However, at the time, the limit of transmission of electric power was 80 miles (130 km), and there were few customers (mostly mines) within that limit. Edison allowed land options it held on the river to lapse—including an option for what became the site of Hoover Dam.

The amount of electricity generated by Hoover Dam has been decreasing along with the falling water level in Lake Mead due to the prolonged drought in the 2010's and high demand for the Colorado River's water. Lake Mead fell to a new record low elevation of 1,071.61 feet (326.63 m) on July 1, 2016 before beginning to rebound slowly.