A thermocline is a distinct layer in a body of water where the temperature changes rapidly with depth. In oceans and large lakes, the upper layer, known as the epilimnion, is warmer and mixed by wind, while the deeper layer, called the hypolimnion, is colder and denser. The thermocline acts as a barrier, preventing mixing between these layers. Thermoclines are important for aquatic life, as they influence the distribution of nutrients and oxygen. Many fish and other organisms prefer specific temperature ranges, so the presence of a thermocline can affect their behavior and habitat. Understanding thermoclines is crucial for studying ecosystems in oceans and lakes.