Another definition is a body of fresh or salt water of considerable size that is surrounded by land.
On Earth a body of water is considered a lake when it is inland, not part of the ocean, is larger and deeper than a pond.
[1][2] A reservoir (etymology from French réservoir a "storehouse [3]) is an artificial lake used to store water.
Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such a brickwork or cast concrete.
Swimming, fishing, and/or boating are permitted in some of these lakes, but not all.