The Reservoir reference article from the English Wikipedia on 24-Apr-2004
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Reservoir

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A reservoir is an artificial lake created by flooding land behind a dam. Some of the world's largest lakes are reservoirs.

Surveyors have to find river valleys which are deep and narrow; the valley sides can then act as natural walls. The best place for building a dam has to be determined. If necessary, humans have to be rehoused and/or historic sites have to be moved, e.g. the temples of Abu Simbel before the construction of the Aswan Dam, creating Lake Nasser.

A reservoir may also be an accumulation of oil or gas beneath the Earth's surface.

See also: List of reservoirs and dams