Lakes

Lakes are inland bodies of standing water. They are typically larger than ponds and persist year-round, though there is no universally agreed size boundary. Lakes form through processes such as tectonic subsidence, glacial sculpting, volcanism, landslides, or riverine alteration that creates basins. They can be natural or artificial; many lakes in populated regions are reservoirs created by damming rivers.

Hydrologically, lakes receive water from rainfall, snowmelt, streams, and groundwater, and lose water through evaporation, seepage, and outflow to rivers or groundwater. Water balance and inflow-outflow dynamics influence size, depth, and seasonal changes. In temperate climates many lakes undergo thermal stratification in summer, with a warm upper layer and a cooler bottom layer; mixing events, called turnover, help distribute oxygen and nutrients.

Ecologically, lakes host diverse communities of algae, aquatic plants, invertebrates, fish, and amphibians. They are categorized by productivity: oligotrophic (nutrient-poor and clear), mesotrophic, and eutrophic (nutrient-rich and often turbid). Littoral zones near shore support vegetation and invertebrates; deeper zones are dimly lit and support different communities. Lakes are sensitive to pollution, nutrient enrichment, invasive species, and climate change, which can alter their chemistry, temperature regimes, and biodiversity.

Human use includes drinking-water supply, agriculture, fishing, recreation, and hydroelectric power. Management practices focus on protecting water quality, maintaining healthy watershed, monitoring invasive species, and balancing ecological needs with development.

Notable lake types include crater lakes, glacial lakes, oxbow lakes, and tectonic lakes, as well as artificial reservoirs formed by damming rivers. Lakes vary widely in size, depth, and ecological character across regions.