Lake

A lake is a large inland body of standing water, surrounded by land and not part of the ocean. Lakes can be natural or artificial and form through a variety of geological and hydrological processes, including glacial carving, tectonic subsidence, volcanic activity, sediment infilling in basins, or the damming of rivers. They vary widely in size, depth, and water chemistry; most are freshwater, but some are saline, brackish, or mineral-rich due to evaporation or mineral inputs.

Water balance in a lake is governed by precipitation, evaporation, inflows and outflows, and interactions with groundwater. Lakes can exhibit thermal stratification, with a warmer upper layer and a cooler deeper layer; in many temperate regions they undergo annual turnover that mixes nutrients and oxygen throughout the water column.

Ecology and productivity in lakes depend on nutrient availability, light, temperature, and food webs. Lakes host a diversity of algae, aquatic plants, invertebrates, fish, and birds. Excess nutrients can lead to eutrophication, algal blooms, and oxygen depletion in bottom waters.

Common lake types include glacial lakes formed by past ice sheets; crater lakes in volcanic craters; tectonic or fault basins; oxbow lakes created by river meanders; and man-made reservoirs created by damming rivers.

Human use and significance include supplying drinking water, irrigation, hydroelectric power, fishing, transportation, recreation, and cultural or aesthetic value. Lakes support biodiversity and provide ecosystem services such as water purification, climate moderation, and groundwater recharge.

Environmental pressures include nutrient pollution, sedimentation, invasive species, acidification, and climate-change-related changes in ice cover, evaporation, and water temperature. Conservation and integrated watershed management aim to maintain water quality and ecological health while balancing human needs.