Reservoir

A reservoir (/ˈrɛzərvwɑːr/; from French réservoir [ʁezɛʁvwaʁ]) is an enlarged lake behind a dam, usually built to store fresh water, often doubling for hydroelectric power generation.

Reservoirs are created by controlling a watercourse that drains an existing body of water, interrupting a watercourse to form an embayment within it, excavating, or building any number of retaining walls or levees to enclose any area to store water.