The epilimnion is the upper layer of water in a stratified lake or pond. It is typically warm and well-mixed due to wind action, which helps distribute heat and oxygen. This layer is crucial for aquatic life, as it supports various organisms, including phytoplankton and zooplankton, that thrive in sunlight. Beneath the epilimnion lies the metalimnion, or thermocline, where temperature changes rapidly with depth. The distinct temperature gradient between the epilimnion and the deeper layer, known as the hypolimnion, affects the overall ecology of the water body. Understanding these layers is essential for studying freshwater ecosystems.