Yahoo TV

Bleached-white embankments all around the dam, an engineering marvel that symbolized the American ascendance of the 20th Century, show how far the water level has dropped from its usual level.

Lake Mead is the largest reservoir in the United States. It is crucial to the water supply of 25 million people including in the cities of Los Angeles, San Diego, Phoenix, Tucson and Las Vegas. Hoover Dam generates hydroelectric power to serve 1.3 million people in the states of Nevada, Arizona and California.

Patti Aaron, a spokeswoman for the Bureau of Reclamation's Lower Colorado Region, said: "The lake was about 95 percent full in year 2000, and now we're at thirty five percent."

John Lingenfelter, 63, visiting the dam from Phoenix, Arizona, remembers a time when the water level was much higher and says it makes him "very concerned about the future of the Earth itself."

37-year-old Carlos Farias, a recreational fisherman at Lake Mead, said: "Five months ago, the water level used to be right above this flat land right here about five months ago..."