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. Construction of the Aswan Dam in Egypt flooded several ancient Nubian sites, some of which were relocated to safe places as far away as Madrid, Spain.