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Hypolimnion
Bottom layer of water in a thermally-stratified lake / From Wikipedia, the free encyclopedia
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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.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Lake_Stratification_%2811%29.svg/320px-Lake_Stratification_%2811%29.svg.png)
I. The Epilimnion
II. The Metalimnion
III. The Hypolimnion
The scales are used to associate each section of the stratification to their corresponding depths and temperatures. The arrow is used to show the movement of wind over the surface of the water which initiates the turnover in the epilimnion and the hypolimnion.
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.