As the temperature increases in the spring, the lake water divides into an upper half which is warm ( epilimnion ), while the lower half ( hypolimnion ) stays cold and lacking in oxygen.
12.
The northwest to southeast orientation of Uvas Reservoir is in line with prevailing winds which drive the warm surface layer ( epilimnion ) down into the cool bottom layer ( hypolimnion ), so that by late summer the bottom water is warm and anoxic.
13.
"' Lake stratification "'is the separation of lakes into three layers : 1 ) Epilimnion-top of the lake; 2 ) Metalimnion ( or thermocline )-middle layer that may change depth throughout the day; 3 ) and the Hypolimnion-the bottom layer.
14.
In all but the shallowest lakes, there are major changes in the chemical composition of lake water at different depths, especially during the summer months when many lakes stratify into a warm, well oxygenated upper layer ( " epilimnion " ) and a cool de-oxygenated lower layer " ( hypolimnion " ).
