This is called fall overturn . The top layer is the coldest. When the surface of the lake freezes, the water underneath is protected from wind and heat loss. About 80 percent of all the lake water in the world can be found in 40 large lakes and 70 percent of all the lake water in the world is found in North America, Africa, and Asia. The deepest freshwater lake in the world is Lake Baikal in Siberia.
Lake Superior is the largest freshwater lake in the world.
Parts of Lake Superior are in Michigan, Minnesota, Wisconsin and Ontario, Canada. Lake effect snow happens when a cold air mass passes for long distances over warmer lake water. The air picks up moisture and heat from the lake. When the air mass reaches the lake shore, it often drops the moisture as snow. The Great Lakes generate lots of lake effect snow for surrounding areas.