Lake turnover is the process of a lake’s water turning over from top to bottom.This occurs when the layers of water with noted temperature differences begin to mix together and the water and debris that has been sitting at the bottom of the lake begins to mix with the layers of water above it.
During the summer, the surface layer is the warmest. It is heated by the sun. During the fall, the warm surface water begins to cool. As water cools, it becomes more dense, causing it to sink. The deepest layer is the coldest. The sun’s radiation does not reach this cold, dark layer. This dense water forces the water of the lowest layer to rise, “turning over” the layers.
This has implications for a lake’s structure because the denser water is heavier and will be at the bottom of a lake while the less dense water is lighter and will generally be at the top of the lake.
As nutrients are available at the surface of the water again and the sun gets stronger, the first algae are able to grow. The lake’s clarity will increase, and then decrease again as the new algae growth temporarily clouds the water.
This phenomenon is nature’s own way of ‘mixing things up’ as the seasons change to allow new growth of algae and fish, all of which contribute to the health and diversity of the lake.