|All About Ponds and
Water temperatures in lakes during summer months is not uniform from top to bottom. Three distinct layers develop: The top layer stays warm at around 6575 degrees F (18.824.5 degrees C). The middle layer drops dramatically, usually to 4565 degrees F (7.418.8 degrees C). The bottom layer is the coldest, staying at around 3945 degrees F (4.07.4 degrees C). Since light does not penetrate to the bottom, photosynthesis is limited to the top layer. Because of the warmer waters and more plentiful food supply, almost all creatures spend the summer months in the upper layer.
During spring and fall the lake temperature is more uniform. Fish and other animals are found throughout the layers of the lake.
Even in cold climates, most lakes are large enough so that they don't freeze solid, unlike ponds. During the winter months some creatures hibernate in the bottom mud. Some fish continue to feed, but less actively. A layer of ice can develop on the top of lakes during winter. The ice blocks out sunlight and can prevent photosynthesis. Without photosynthesis, oxygen levels drop and some plants and animals may die. This is called "winterkill."