Thermoclines are traditionally linked to summer stratification in northern natural lakes that freeze over. The ice melts and spring turnover follows, the surface water warms creating the upper epilimnion layer, then the deeper water cools down rapidly creating the thermocline or metalimnion layer or summer stratification.
Winter period in a deep highland reservoir is very deferent than a northern natural lake. The warm summer water slowly cools down and sinks through the warmer upper layers, cooling down the water column. The heavier cool water presses down a layer of warmer water that is trapped between two colder layers, the winter thermocline or life zone for bass during the cold water period. Some bass will venture up to sunny banks during the cold water period to feed on cold water prey fish, however will move down to the warmest layer with sufficient DO, dissolved oxygen, and prey fish the majority of the time. The exception to this is in shallow lakes, rivers and power generation lakes where the water has current or too shallow to layer.
This is why it is very important to have good electronics during the winter period to locate the "life zone" where the deep bass are holding. The deep highland or hill land reservoirs commonly have bass schools holding in water 40 to 60 foot depths that go un fished during the cold water periods. Dirty or muddy surface water is just that, dirty surface water and for me something to be avoided during cold water periods, unless it is the warmest water available.
Tom
