A dam is a barrier designed and constructed to contain the flow of water. It is often built in conjunction with a hydroelectric power station to provide electricity.

Dams are built for purposes such as generating hydroelectricity, creating recreational areas, minimizing flood risks, diverting water for irrigation, and providing water for towns and cities.

The type of dam built in any given situation depends on factors such as the intended purpose, environmental considerations, available finances and the location.

Different types of dams include masonry dams, embankment dams and arch-gravity dams.

Beavers create their own dams from sticks and mud as protection from predators and also to help provide easy access to food.

Dams are huge engineering projects that require vast financial resources. For example, the construction of the Itaipu Dam on the border of Brazil and Paraguay (completed in 1984) cost around US$20 billion.

Built along the Colorado River between 1931 and 1936, The Hoover Dam reaches 726 feet in height (221 metres).

When the Hoover Dam was completed it was both the world’s largest concrete structure and largest hydroelectric power station.

The Hoover Dam is made of enough concrete to make a two lane highway from New York to San Francisco, that’s around 4000 miles (2500 kilometres).

As of 2010, the tallest dam in the world is Nurek Dam in Tajikistan. Completed in 1980, it reaches 300 metres (984 feet) in height.

Many dam failures have occurred in the past, these disasters can cause significant damage and threaten lives.

In 1889 a failure of the South Fork Dam near Johnstown, Pennsylvania, USA, killed over 2200 people.

In 1975, the Banqiao Dam in China was among many dams that were destroyed after the extreme rains of Typhoon Nina. It is estimated that between 90000 and 230000 lives were lost as a result of the Banqiao Dam breaking.