The warm upper layer of a body of water with thermal stratification, which extends down from the surface to the Thermocline, which forms the boundary between the warmer upper layers of the emilimnion and the colder waters of the lower depths, or Hypolimnion. The epilimnion is less dense than the lower waters and is wind-circulated and essentially homothermous. Also see Thermal Stratification, Fall Overturn, and Spring Overturn.
The upper layer of water in a thermally stratified lake or reservoir. This layer consists of the warmest water and has a fairly uniform (constant) temperature. The layer is readily mixed by wind action.
