The fall turnover is a phenomenon poorly understood by many anglers. It is most noticeable in bodies of water that have significant depth and layers of markedly different temperature. This is generally true of large lakes and reservoirs. However, smaller bodies of water can also turn over.

Lake Zones

During the summer, lake water stratifies in epilimnion, thermocline, and hypolimnion zones. The epilimnion, or upper level, is warmest and contains the greatest amount of dissolved oxygen.


The thermocline, or middle level, is lower in temperature and dissolved oxygen. The hypolimnion, or lower level, has the coolest temperature and the least (perhaps little or no) dissolved oxygen. New oxygen remains in the upper layers and may be prevented from reaching deeper levels by the thermocline.

Most gamefish avoid the lower level or the deeper parts of it. Low oxygen, and the fact that the bottom of many lakes contain decaying matter that is poor for most gamefish and their prey, are major reasons.

Why and How Lakes Turn

In the fall, the weather turns cooler. When the average air temperature is lower than the water’s surface, the temperature in the upper zone declines and mixing takes place. Cold water is more dense than warm water, so newly cooled surface water sinks to deeper levels. This causes a mixing of the water throughout the zones, and eventually the zones disappear. When the water column mixes completely, the temperature is virtually the same from top to bottom. This phenomenon is the actual “turnover.” Complete mixing may take several weeks to occur, or it may occur very quickly.

A severe cold front can drop surface water temperature dramatically, perhaps even 10 degrees, virtually in a day; this hastens turnover.

There is disagreement as to whether wind plays a role in the turnover process. Although wind doesn’t cause turnover, some texts on this subject written by biologists say that wind aids the mixing.

In any case, mixing often causes new turbidity in the water for a while. You may also notice suspended leaves and other matter in the water, which is the result of decaying bottom matter that was in the lower zone being dispersed through all levels.

When Lakes Turn

The time sequence for fall turnover varies geographically, occurring later the further south one goes. Obviously, lakes in the far north cool down first. Some southern lakes don’t actually stratify at all, so this phenomenon may not occur, and impoundments that see considerable water level fluctuation likewise may not have distinct zones and thus no turnover. Turnover is less likely or less pronounced in places where there’s no distinct seasonal weather change or where fall weather is very mild.

Where smaller and larger lakes exist in the same general area, smaller ones may turn over before larger ones, or the speed with which they turn over may be quite different. Thus, where there are lakes relatively near each other, fishing in one can be much better or much worse than in another. Since fishing is often poor during the turnover, if you have options as to where to fish, try to determine what the status is of those places you could visit. Biologists from regional state fisheries offices, and workers at local boat docks and tackle shops, are a good source of information.