A
reservoir (
etymology: from
French réservoir a "storehouse" ) is an enlarged natural or
artificial lake,
storage pond or
impoundment created using a
dam or
lock to store water. Reservoirs can be created by controlling a stream that drains an existing body of water. They can also be constructed in river valleys using a dam. Alternately, a reservoir can be built by excavating flat ground and/or constructing
retaining walls and
levees.