Lake

A lake is a body of water surrounded by land and occupying a depression or basin in the Earth's surface. Lakes vary greatly in size, depth, and shape. Some receive water mainly from rivers, streams, rainfall, or melting snow. Others lose water through an outlet river, evaporation, or seepage into the ground.

Most are freshwater, but some are salty when evaporation is high and little water flows out. Lakes can form in several ways. Glaciers may carve basins that later fill with water, while volcanic activity can create lake-filled craters or calderas. Tectonic movements can form deep basins, while landslides may block valleys and retain water.

A lake is connected to the landscape around it through the movement of water, sediments, and nutrients. Conditions also change with depth: light, temperature, and oxygen are not the same everywhere, so different organisms occupy different zones. Algae and aquatic plants use sunlight to produce food, while fish, invertebrates, amphibians, birds, and microorganisms form food webs.

Lakes store water, influence local temperatures, and support agriculture, water supplies, fishing, transport, and recreation. Their ecosystems can be disturbed by pollution, excess nutrients, introduced species, water withdrawal, and climate change. These pressures may alter water temperature, oxygen levels, and the amount of water in the lake.