Hypolimnion
Bottom layer of water in a thermally-stratified lake / From Wikipedia, the free encyclopedia
The hypolimnion or under lake is the dense, bottom layer of water in a thermally-stratified lake.[1] The word "hypolimnion" is derived from Ancient Greek: λιμνίον, romanized: limníon, lit. 'lake'.[2] It is the layer that lies below the thermocline.
Typically the hypolimnion is the coldest layer of a lake in summer, and the warmest layer during winter.[1] In deep, temperate lakes, the bottom-most waters of the hypolimnion are typically close to 4 °C throughout the year. The hypolimnion may be much warmer in lakes at warmer latitudes. Being at depth, it is isolated from surface wind-mixing during summer,[3] and usually receives insufficient irradiance (light) for photosynthesis to occur.