Lake structure.

The shallowest waters along the lake shore, where rooted aquatic plants may grow, is called the littoral zone. Beyond the littoral zone in the open lake is the limnetic zone. Lakes are generally divided vertically into three main depth zones. The epilimnion is the warm surface layer of lakes. Below the epilimnion is the thermocline, or metalimnion. The thermocline is a zone through which temperature changes substantially with depth, generally about 1°C per meter of depth. Below the thermocline are the cold dark waters of the hypolimnion. Each of these zones supports a distinctive assemblage of lake organisms.