What is the name of the upper thermal stratification layer in a lake?

The upper thermal stratification layer in a lake is known as the epilimnion. This layer is characterized by warmer temperatures and is well-mixed due to wind action, promoting oxygenation and supporting aquatic life, such as fish and phytoplankton. The epilimnion typically sits above the thermocline, which is the layer (or transition zone) that separates the warm upper layer from the cooler depths of the lake.

In contrast, the metalimnion is a middle layer where temperature changes rapidly with depth, while the hypolimnion refers to the colder, denser water at the bottom of the lake. Understanding these layers is crucial in water quality management, as they influence stratification patterns, temperature variations, and the distribution of nutrients and dissolved oxygen within the water body.