There is little mixing across these layers during stratification and each layer retains its unique composition. In the fall, winds blow and waves begin to disturb these layers. The water cools and, in what is called the fall overturn, the temperature zones break down, and the lake's water mixes completely. During the winter, the waters stay mixed, but, come spring, the sun warms the top layer and the lake's waters stratify again. Watersheds and their Lakes A watershed is the area of land that drains to a lake or other water body.
Watersheds vary in size from just a couple of acres to thousands of square miles.
The characteristics of a watershed and the land use activities within it have profound effects on lakes. If a hillside is clear cut or a wetland drained, a lake may receive significant pollution loads or its water cycle may be altered. Changing from undeveloped to residential land uses may result in a 700-percent increase in phosphorus loading to a lake. Much of this increase can be traced to the loss of forests and the removal of plant material- both of which naturally bind phosphorus, keeping it out of lakes and other water bodies. Other sources of phosphorus in lakes include failing septic systems and activities such as car-washing and landscaping.