Does the Lake Turn Over?

According to the Missouri Department of Conservation, it does - twice a year. Water is densest at 39 degrees Fahrenheit. In the spring, when the surface temperature warms up to 39 degrees, it becomes heavier than the water below, and it begins to sink. That forces the water on the bottom to rise. The process can go on for up to several weeks if the weather is cool and windy. When the water temperature reaches about 50 degrees, the water stratifies into layers and turnover ceases.

Conversely, in autumn, when the surface temperature falls to about 50 degrees, the water begins to sink and create a circulation known as fall turnover. As water moves upward from the bottom in the fall, it sometimes carries sulfur dioxide gas from rotting vegetation. This can give off a hint of rotten egg odor on the surface. Fall turnover can last several weeks, especially if enhanced by windy weather. The process is complete by the time ice forms on the surface.

Whether it occurs in spring or fall, lake turnover affects oxygen levels in the water. Since fish seek out areas of greater oxygen, you will find them near the bottom in the winter and closer to the surface in summer. During the turnover periods, when the oxygen is circulated with the water, fish are apt to be found at any depth.

© 2009 by Michael Gillespie. All rights reserved.