Reservoir

Lake Vyrnwy reservoir in Wales

A reservoir is an artificial lake built to hold fresh water.

A river is dammed to stop the water flowing down as usual. Over time the water level behind the dam grows, forming the reservoir. Water flowing past the dam is at a more controlled level.

A bad thing about reservoirs is that constructing them means flooding land where people might live. For example, the construction of Llyn Celyn in north Wales required the destruction of a small village named Capel Celyn.