The Hoover Dam, is a concrete arch dam on the Colorado River close to Las Vegas in the southwest of the United States. It is sited in a near-desert region. It was opened in 1936, when it was the world’s largest hydro-electric power generating station. After all these years, it is still the world’s 38th-largest hydro-electric generating station. The reservoir created by the dam is called Lake Mead.

The Hoover Dam is in an area of extreme natural beauty for, just upriver of Lake Mead is the Grand Canyon. Matching the needs of people for water and power, while looking after the environment, has always been a big challenge. But the dam was actually built for one main purpose: to employ thousands of people during the dark days known as the Depression, when huge numbers of Americans were out of work.

The dam is named after the US President of the time the dam was planned. The Lake is named after the director of the building of the dam.

This curved dam is hollow. It is fitted inside a canyon cut by the river. It is very tall and narrow. The dam was an enormous challenge. For example, concrete gives out heat as it sets. If it can’t give out the heat, it doesn’t set. You wouldn't normally notice this, but when you pour huge amounts of concrete, it becomes a major problem, and refrigeration pipes had to be placed inside the concrete to cool it down. Without the cooling it would have taken the concrete 125 years to set. There is enough concrete in the dam to pave a two-lane road from San Francisco to New York.

The dam was built by first digging four huge diversion tunnels (each 17m across) in the sides of the canyon. These took the whole of the river water. Then the dam was begun.

The power turbines are inside the dam and can be seen on conducted tourist visits. The whole of the river goes through the turbines. Nothing goes over the top or around the sides. When the water gets to the bottom of the penstocks it is traveling at nearly 140km/hr. The electricity goes to help power the city of Los Angeles. River water goes to irrigate farmland.

Facts: Dam length 379m; dam height 221m; Lake Mead surface area 640sq km; power generation 2078MW.