Typically stratified lakes show three distinct layers: the epilimnion, comprising the top warm layer; the thermocline (or metalimnion), the middle layer, whose depth may change throughout the day; and the colder hypolimnion, extending to the floor of the lake.

In the field of limnology, the thermal stratification of a lake creates three distinct layers, primarily during the warmer summer months. The top layer is the epilimnion, which is the warmest, least dense, and most oxygen-rich part of the lake as it interacts directly with the atmosphere and sunlight. Beneath it lies the metalimnion, often referred to as the thermocline; this is a thin, transitional middle layer where the temperature drops rapidly with depth. The deepest and coldest layer is the hypolimnion, which is highly dense and often isolated from the surface, sometimes becoming oxygen-depleted because wind cannot mix atmospheric air down into it. Biologically, lakes are also divided into the photic zone, where light allows for photosynthesis, and the aphotic zone, the dark depths where light cannot reach. These layers typically "turn over" in the spring and autumn when temperatures equalize, allowing the entire body of water to mix and refresh its nutrient levels.