A lake is a large body of standing water that occupies an inland basin. Lakes are temporary water bodies that are smaller than seas and oceans. They are not fast-moving like rivers or as small as ponds. Lakes can form through various mechanisms, including: * Wind action * Animal activity * Meteorite impacts * Glaciation * Tectonic depressions Lakes are a source of fresh water for household, agricultural, and industrial uses, and are susceptible to changes in chemical composition because of these uses and other factors.

How are lakes different from rivers and oceans?

Lakes, rivers, and oceans are all bodies of water, but they differ significantly. Lakes are inland bodies of standing or slowly moving water occupying a basin of appreciable size. Rivers and streams are characterized by relatively fast movement. Oceans are much larger and deeper than seas, covering nearly 71% of Earth’s surface. Lakes depend on a balance between water sources and losses, with major inputs from streams, rivers, precipitation, and groundwater. Lakes interact with the atmosphere and the materials of their basins. Rivers, however, can be regulated using dams, storage reservoirs, and diversions. The most important physical characteristic of most lakes is their pattern of temperatures, especially the changes of temperature with depth.

What are some common ways that lakes are formed?

Lakes form through various mechanisms, including tectonic activity , which can create large basins through crustal movement or uplift that interferes with drainage patterns. Volcanic activity can also lead to lake formation when volcanic craters or calderas collapse and fill with water. Landslides can block drainage depressions, creating lake basins. Glaciation is another significant factor, with glaciers carving out basins through mechanical action and damming effects. Additionally, fluvial processes , such as river action and sediment deposition, can contribute to lake formation, as can wind action through dune construction and erosion. Even animal activity , like beavers building dams, and meteorite impacts can result in lake basins.

How do lakes get and lose their water?

Lakes gain water from various sources such as streams and rivers, direct precipitation, and groundwater flow. In some instances, glacier melt can directly contribute to a lake's water volume. The amount of water coming from streams and rivers varies with precipitation and snowmelt. Groundwater reaches lakes through general seepage or springs. Lakes lose water through surface or groundwater flows and evaporation. Lakes without these outflows only lose water through evaporation, which increases their salinity. Evaporation occurs due to vapour pressure differences above the water, influenced by wind speed and thermal convection.

Why are lakes important for wildlife and people?

Lakes are vital for both wildlife and people because they support complex ecosystems and provide essential resources. Lakes offer habitats for diverse plant and animal species, from microscopic algae to fish, and serve as key wintering and migration stopover locations for birds. For humans, lakes are crucial sources of water for drinking, irrigation, and industrial uses. They also support commercial fisheries and offer recreational opportunities such as boating, fishing, and swimming, contributing to tourism and local economies. However, these uses can also lead to pollution and habitat degradation, highlighting the need for sustainable management to preserve lake ecosystems.

How can human activities affect the health of a lake?

Human activities can significantly degrade lake health through multiple pathways. Sewage and agricultural runoff introduce excessive nutrients, such as nitrates and phosphates, leading to eutrophication . This process encourages algal blooms, which, upon decomposition, deplete oxygen levels, harming aquatic life. Additionally, toxic chemicals, industrial wastes, and petroleum discharge, stemming from human interference, severely affect the quality of the hydrosphere . The introduction of invasive species through global commerce can disrupt the ecological balance, reducing biodiversity and harming native species.

lake

Introduction
General considerations
- Occurrence
- Uses and abuses of lakes
  - Economy and ecology
  - Problems and effects
Lake basins
- Classification of basins
  - Basins formed by tectonism, volcanism, and landslides
  - Basins formed by glaciation
  - Basins formed by fluvial and marine processes
  - Basins formed by wind action, animal activity, and meteorites
- Topography of basins
- Sediments and sedimentation
  - Clastic sediments
  - Chemical precipitates
Lake waters
- Chemical composition
  - Salinity, nutrients, and oxygen
  - Carbon dioxide
  - Sulfates, nitrates, and phosphates
- Thermal properties
  - Vertical mixing and overturn
  - The heat budget of lakes
  - Heat transfer
Lake hydraulics
- Currents
  - Pressure gradients
  - Wind stress
  - Internal waves and Langmuir circulation
- Surface waves
- Seiches
  - Cause and characteristics
  - Internal seiches
- Effects of wave and current action
  - Shore erosion and coastal features
  - Bottom morphology
The hydrologic balance of the lakes
- The water budget
  - Water input
  - Water output
  - Water level fluctuations
- Lake extinction
Major natural lakes of the world

References & Edit History Quick Facts & Related Topics

Images & Videos

Lake Ann in North Cascades National Park, Washington

Two illustrated divers are superimposed onto a photograph showing a lake underwater.

Join a Climate-Change Research Team Collecting Samples from the Bottom of Greenland's Arctic Lakes

Ice-covered rocks line the frozen shoreline of Lake Huron in Michigan, with distant trees, houses, and a water tower visible along the horizon.

Two wooden dugout canoes rest on the sandy shore of Lake Tanganyika, Tanzania, with blue water and distant hills in the background.

At a Glance

lake summary

lake

physical feature

Also known as: inland sea, landlocked sea

Written by

Robert K. Lane

Fact-checked by

Britannica Editors

Last updated

Oct. 31, 2026 •History

News •

3,300-year-old sword discovered in an Italian lake may have been dumped there on purpose — and it's still sharp • Oct. 28, 2026, 5:27 PM ET (Live Science)

lake, any relatively large body of slowly moving or standing water that occupies an inland basin of appreciable size. Definitions that precisely distinguish lakes, ponds, swamps, and even rivers and other bodies of nonoceanic water are not well established. It may be said, however, that rivers and streams are relatively fast moving; marshes and swamps contain relatively large quantities of grasses, trees, or shrubs; and ponds are relatively small in comparison with lakes. Geologically defined, lakes are temporary bodies of water. For a list of the major natural lakes of the world, see below.

This article treats lake basins and sedimentation; the physical and chemical properties of lake waters; lake currents, waves, and tides; and the hydrologic balance of lakes. For information on related systems, see river. The place of lakes within the hydrologic cycle is further dealt with in hydrosphere, as are certain aspects of lake sedimentation and water chemistry. See inland water ecosystem for information on lacustrine life-forms.

General considerations

Occurrence

Within the global hydrologic cycle, freshwater lakes play a very small quantitative role, constituting only about 0.009 percent of all free water, which amounts to less than 0.4 percent of all continental fresh water. Saline lakes and inland seas contain another 0.0075 percent of all free water. Freshwater lakes, however, contain well over 98 percent of the important surface waters available for use. Apart from that contained in saline bodies, most other continental waters are tied up in glaciers and ice sheets and the remainder is in groundwater.

Four-fifths of the 125,000 cubic km (30,000 cubic miles) of lake waters occur in a small number of lakes, perhaps 40 in all. Among the largest are Lake Baikal, in Central Asia, containing about 23,000 cubic km (5,500 cubic miles) of water; Lake Tanganyika (19,000 cubic km [4,600 cubic miles]), in eastern Africa; and Lake Superior (12,000 cubic km [2,900 cubic miles]), one of the Great Lakes of North America. The Great Lakes contain a total of about 25,000 cubic km (6,000 cubic miles) of water and, together with other North American lakes larger than 10 cubic km (2 cubic miles), constitute about one-fourth of the world’s lake waters. The Caspian Sea, though not considered a lake by some hydrologists, is the world’s largest inland sea. Located in Central Asia, the Caspian Sea has an area of about 386,000 square km (149,000 square miles).

Although lakes are to be found throughout the world, the continents of North America, Africa, and Asia contain about 70 percent of the total lake water, the other continents being less generously endowed. Lakes also occur far beneath the ice sheets of Antarctica; however, surveys of the volume and other features of those discovered so far remain incomplete. One-fourth of the total volume of lake water is spread throughout the world in uncounted numbers of small lakes. Anyone who has flown over much of the Canadian plains area cannot help but be struck by the seemingly endless skein of lakes and ponds covering the landscape below. Though the total volume of water involved is comparatively small, the surface area of lake water is substantial. The total surface area of all Canadian lakes has been estimated to exceed the total surface area of the province of Alberta. The U.S. state of Alaska has more than three million lakes with surface areas greater than 8 hectares (20 acres).

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International Waters

The larger, deeper lakes are a significant factor within the cycle of water—from rain to surface water, ice, soil moisture, or groundwater and thence to water vapour. These lakes receive the drainage from vast tracts of land, store it, pass it on seaward, or lose it to the atmosphere by evaporation. On a local basis, even the smaller lakes play an important hydrologic role. The relatively high ratio of exposed surface area to the total water volume of these lakes accentuates their effectiveness as evaporators. In some cases the efficiency of lakes in losing water to the atmosphere is locally undesirable, because of public and industrial requirements for lake water. A striking example of this condition is the Aral Sea, located in Central Asia. Although it is still one of the world’s largest bodies of inland water, in the second half of the 20th century its area was reduced by two-fifths and its mean surface level had dropped by more than 12 metres (40 feet), primarily as a result of the diversion of the Syr Darya and Amu Darya rivers for irrigating adjoining fields. In some basins (e.g., the Chad basin in Africa), lakes are the terrestrial end point of the hydrologic cycle. With no outflow downstream toward the oceans, these closed lakes swell or recede according to the balance of local hydrologic conditions.

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General considerations

Occurrence

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