In the study of limnology, the three distinct thermal layers of a stratified lake are the Epilimnion, the Metalimnion, and the Hypolimnion. The Epilimnion is the top layer; it is the warmest because it is directly heated by the sun and mixed by the wind, making it the most oxygen-rich part of the lake where most fish and swimmers spend their time. The Metalimnion is the middle layer, which contains the thermocline—the specific depth where the water temperature drops most rapidly as you go deeper. Finally, the Hypolimnion is the bottom layer; it is cold, dense, and largely shielded from the sun's heat. This stratification is most pronounced during the summer months. In the spring and fall, many temperate lakes undergo a process called "turnover," where the layers mix completely as surface temperatures change, redistributing oxygen and nutrients throughout the entire water column. This cycle is essential for maintaining a healthy aquatic ecosystem in deep-water lakes.