The Fall Turnover

Most of us know that the turnover is simply when the water on the top becomes cooler and therefore heavier than the water on the bottom it sinks causing the warmer bottom water to rise, therefore the “turnover”.  Lakes that have little deep water or sufficient current to properly mix the water will not stratify.

Lets see what actions cause this reaction: As the Summer sun beats down on the cool water starting to raise the surface temp. into the 80’s and above a stratification occurs that separates the water into 3 separate layers.

The lightest and warmest water at the top is called the upper or epilimnion layer, by mid to late summer this super heated water although usually fairly well oxygenated by wind and currents can become too hot for comfort.

The bottom of the three layers known as the hypolimnion layer is the coolest of the three layers but also has the least usable oxygen of the three so does not hold any fish.

The middle layer known as the thermocline or metalimnion layer is the most acceptable to fish as it has the best mix of water temp. and oxygen making it the most comfortable of the layers.

So we have the lightest and hottest water at the top, the coolest and heaviest at the bottom and the most comfortable in the middle.

So what we see in the Fall is actually a turning over of the water, as the cool air drops the temp. in the upper layer down below that of the two lower levels causing it to sink thru the thermocline into the bottom layer they simply change places. Then the cool rains and winds cause a mix and the waters combine again into one relatively stable column of water with the temp. about the same through out the water column.  Sometimes this happens so fast that the bottom layer will bring up debris from the bottom causing a dingy look to the water and a strong smell for a few days.

This period can lasts from a few days to a couple of weeks and play havoc with the fish bite.  Hope this helps you to understand the “Fall Turnover.”

Earnie (Papa) Cella

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