The deep water of a lake's profundal zone is called the epilimnion water temperature is briefly uniform at all depths, and winds create vertical currents during the spring overturn at the water temperature changes abruptly over a narrow depth range. thermocline the epilimnion cools, becomes denser, and sinks, eliminating the thermocline during the hypolimnion the top layer of the limnetic zone is called the and is heated by the sun in summer. fall overturn