Blowdown Lake in the mountains near Pemberton, British Columbia

Oeschinen Lake in the Swiss Alps

A lake (from Latin lacus) is a terrain feature (or physical feature) that is an considerable inland body of water, not part of the ocean, that is larger and deeper than a pond, and may or may not be moving slowly, and is localized to the bottom of basin (another type of landform or terrain feature) and is fed by a river.^[3]. Small lakes are also much more numerous than big lakes: in terms of area, one third of the world's standing water is represented by lakes and ponds of or less. However, large lakes contribute disproportionately to the area of standing water with 122 large lakes of 1,000 square kilometres (390 sq mi, 100,000 ha, 247,000 acres) or more representing about 29% of the total global area of standing inland water.

Meaning and usage of "lake"

There is considerable uncertainty about defining the difference between lakes and ponds. For example, limnologists have defined lakes as waterbodies which are simply a larger version of a pond, or which have wave action on the shoreline, or where wind induced turbulence plays a major role in mixing the water column. None of these definitions completely excludes ponds and all are difficult to measure. For this reason there has been increasing use made of simple size-based definitions to separate ponds and lakes. In the United Kingdom, for example, the charity Pond Conservation - which works to protect all types of freshwater ecosystem - has defined lakes as waterbodies of or more in area ^[4]. Elsewhere, other workers have treated lakes as waterbodies of and above, or and above (see definitions of pond). Charles Elton, one of the founders of ecology, regarded lakes as waterbodies of or more, a value somewhat larger than modern studies would suggest appropriate ^[5]. The term "lake" is also used to describe a feature such as Lake Eyre, which is a dry basin most of the time but may become filled under seasonal conditions of heavy rainfall.

In ecology the environment of a lake is referred to as lacustrine. Large lakes are occasionally referred to as "inland seas", and small seas are occasionally referred to as lakes. Smaller lakes tend to put the word "lake" after the name, as in Green Lake, while larger lakes often invert the word order, as in Lake Ontario, at least in North America. In some places, the word "lake" does not correctly appear in the name at all (e.g., Windermere in Cumbria).

Only one lake in the English Lake District is actually called a lake; other than Bassenthwaite Lake, the others are all "meres" or "waters". Only six bodies of water in Scotland are known as lakes (the others are lochs): the Lake of Menteith, the Lake of the Hirsel, Pressmennan Lake, Cally Lake near Gatehouse of Fleet, the saltwater Manxman's Lake at Kirkcudbright Bay, and The Lake at Fochabers. Of these only the Lake of Menteith and Cally Lake are natural bodies of fresh water.

Distribution of lakes

The vast majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes. More than 60% of the world's lakes are in Canada; this is because of the deranged drainage system that dominates the country.

Finland is known as The Land of the Thousand Lakes, (actually there are 187,888 lakes in Finland, of which 60,000 are large),^[6] and the U.S. state of Minnesota is known as The Land of Ten Thousand Lakes. The license plates of the Canadian province of Manitoba used to claim "100,000 lakes" as one-upmanship on Minnesota, whose license plates boast of its "10,000 lakes."

Most lakes have a natural outflow in the form of a river or stream, but some do not and lose water solely by evaporation or underground seepage or both. They are termed endorheic lakes (see below).

Many lakes are artificial and are constructed for hydro-electric power generation, recreational purposes, industrial use, agricultural use, or domestic water supply.

Evidence of extraterrestrial lakes exists; "definitive evidence of lakes filled with methane" was announced by NASA as returned by the Cassini Probe observing the moon Titan, which orbits the planet Saturn.

Origin of natural lakes

Ipperwash Beach, Lake Huron, Ontario, Canada

There are a number of natural processes that can form lakes. A recent tectonic uplift of a mountain range can create bowl-shaped depressions that accumulate water and form lakes. The advance and retreat of glaciers can scrape depressions in the surface where water accumulates; such lakes are common in Scandinavia, Patagonia, Siberia, and Canada. The most notables examples are probably the Great Lakes of North America.

Lakes can also form by means of landslides or by glacial blockages. An example of the latter occurred during the last ice age in the U.S. state of Washington, when a huge lake formed behind a glacial flow; when the ice retreated, the result was an immense flood that created the Dry Falls at Sun Lakes, Washington.

Salt crystals, on the shore of Lake Urmia, Iran

Small, crescent-shaped lakes called oxbow lakes can form in river valleys as a result of meandering. The slow-moving river forms a sinuous shape as the outer side of bends are eroded away more rapidly than the inner side. Eventually a horseshoe bend is formed and the river cuts through the narrow neck. This new passage then forms the main passage for the river and the ends of the bend become silted up, thus forming a bow-shaped lake.

Crater lakes are formed in volcanic calderas which fill up with precipitation more rapidly than they empty via evaporation. An example is Crater Lake in Oregon, located within the caldera of Mount Mazama. The caldera was created in a massive volcanic eruption that led to the subsidence of Mount Mazama around 4860 BC.

Some lakes, such as Lake Jackson in Florida, USA, come into existence as a result of sinkhole activity.

Lake Vostok is a subglacial lake in Antarctica, possibly the largest in the world. The pressure from the ice atop it and its internal chemical composition mean that, if the lake were drilled into, a fissure could result that would spray somewhat like a geyser.

Most lakes are geologically young and shrinking since the natural results of erosion will tend to wear away the sides and fill the basin. Exceptions are those such as Lake Baikal and Lake Tanganyika that lie along continental rift zones and are created by the crust's subsidence as two plates are pulled apart. These lakes are the oldest and deepest in the world. Lake Baikal, which is 25-30 million years old, is deepening at a faster rate than it is being filled by erosion and may be destined over millions of years to become attached to the global ocean. The Red Sea, for example, is thought to have originated as a rift valley lake.

Types of lakes

One of the many artificial lakes in Arizona at sunset

• Periglacial: Part of the lake's margin is formed by an ice sheet, ice cap, or glacier, the ice having obstructed the natural drainage of the land.
• Subglacial: A lake which is permanently covered by ice. They can occur under glaciers, ice caps, or ice sheets. There are many such lakes, but Lake Vostok in Antarctica is by far the largest. They are kept liquid because the overlying ice acts as a thermal insulator retaining energy introduced to its underside by friction, by water percolating through crevasses, by the pressure from the mass of the ice sheet above, or by geothermal heating below.
• Glacial lake: a lake with origins in a melted glacier.
• Artificial: A lake created by flooding land behind a dam, called an impoundment or reservoir; by deliberate human excavation; or by the flooding of an excavation incident to a mineral-extraction operation such as an open pit mine or quarry. Some of the world's largest lakes are reservoirs.

A man-made lake in Keukenhof, Netherlands

• Endorheic, also called terminal or closed: A lake which has no significant outflow, either through rivers or underground diffusion. Any water within an endorheic basin leaves the system only through evaporation or seepage. These lakes, such as Lake Eyre in central Australia or the Aral Sea in central Asia, are most common in desert locations.
• Meromictic: A lake which has layers of water which do not intermix. The deepest layer of water in such a lake does not contain any dissolved oxygen. The layers of sediment at the bottom of a meromictic lake remain relatively undisturbed because there are no living organisms to stir them up.
• Fjord lake: A lake in a glacially eroded valley that has been eroded below sea level.
• Oxbow: A lake which is formed when a wide meander from a stream or a river is cut off to form a lake. They are called "oxbow" lakes due to the distinctive curved shape that results from this process.
• Rift lake: A lake which forms as a result of subsidence along a geological fault in the Earth's tectonic plates. Examples include the Rift Valley lakes of eastern Africa and Lake Baikal in Siberia.
• Underground: A lake which is formed under the surface of the Earth's crust. Such a lake may be associated with caves, aquifers, or springs.

The crater lake of Volcán Irazú, Costa Rica

• Crater: A lake which forms in a volcanic caldera or crater after the volcano has been inactive for some time. Water in this type of lake may be fresh or highly acidic and may contain various dissolved minerals. Some also have geothermal activity, especially if the volcano is merely dormant rather than extinct.
• Lava: A pool of molten lava contained in a volcanic crater or other depression. Lava lakes that have partly or completely solidified are also referred to as lava lakes.
• Former: A lake which is no longer in existence. Such lakes include prehistoric lakes and lakes which have permanently dried up through evaporation or human intervention. Owens Lake in California, USA, is an example of a former lake. Former lakes are a common feature of the Basin and Range area of southwestern North America.
• Seasonal lake: A lake that exists as a body of water during only part of the year.
• Shrunken: Closely related to former lakes, a shrunken lake is one which has drastically decreased in size over geological time. Lake Agassiz, which once covered much of central North America, is a good example of a shrunken lake. Two notable remnants of this lake are Lake Winnipeg and Lake Winnipegosis.
• Eolic: A lake which forms in a depression created by the activity of the winds.

Characteristics

Lake Mapourika, New Zealand

Changes in the level of a lake are controlled by the difference between the input and output compared to the total volume of the lake. Significant input sources are precipitation onto the lake, runoff carried by streams and channels from the lake's catchment area, groundwater channels and aquifers, and artificial sources from outside the catchment area. Output sources are evaporation from the lake, surface and groundwater flows, and any extraction of lake water by humans. As climate conditions and human water requirements vary, these will create fluctuations in the lake level.

Lakes can be also categorized on the basis of their richness in nutrients, which typically affects plant growth. Nutrient-poor lakes are said to be oligotrophic and are generally clear, having a low concentration of plant life. Mesotrophic lakes have good clarity and an average level of nutrients. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and possible algal blooms. Hypertrophic lakes are bodies of water that have been excessively enriched with nutrients. These lakes typically have poor clarity and are subject to devastating algal blooms. Lakes typically reach this condition due to human activities, such as heavy use of fertilizers in the lake catchment area. Such lakes are of little use to humans and have a poor ecosystem due to decreased dissolved oxygen.

Due to the unusual relationship between water's temperature and its density, lakes form layers called thermoclines, layers of drastically varying temperature relative to depth. Fresh water is most dense at about 4 degrees Celsius (39.2 °F) at sea level. When the temperature of the water at the surface of a lake reaches the same temperature as deeper water, as it does during the cooler months in temperate climates, the water in the lake can mix, bringing oxygen-starved water up from the depths and bringing oxygen down to decomposing sediments. Deep temperate lakes can maintain a reservoir of cold water year-round, which allows some cities to tap that reservoir for deep lake water cooling.

Lake Teletskoye, Siberia

The material at the bottom of a lake, or lake bed, may be composed of a wide variety of inorganics, such as silt or sand, and organic material, such as decaying plant or animal matter. The composition of the lake bed has a significant impact on the flora and fauna found within the lake's environs by contributing to the amounts and the types of nutrients available.

Limnology

Lake Billy Chinook, Deschutes National Forest, Oregon.

A lake moderates the surrounding region's temperature and climate because water has a very high specific heat capacity (4,186 J·kg⁻¹·K⁻¹). In the daytime, a lake can cool the land beside it with local winds, resulting in a sea breeze; in the night, it can warm it with a land breeze.

How lakes disappear

Lake Chad in a 2001 satellite image, with the actual lake in blue, and vegetation on top of the old lake bed in green. Above that, the changes from 1973 to 1997 are shown.

Some lakes can disappear seasonally. These are called intermittent lakes and are typically found in karstic terrain. A prime example of an intermittent lake is Lake Cerknica in Slovenia.

Sometimes a lake will disappear quickly. On 3 June, 2005, in Nizhny Novgorod Oblast, Russia, a lake called Lake Beloye vanished in a matter of minutes. News sources reported that government officials theorized that this strange phenomenon may have been caused by a shift in the soil underneath the lake that allowed its water to drain through channels leading to the Oka River.^[7]

The presence of ground permafrost is important to the persistence of some lakes. According to research published in the journal Science ("Disappearing Arctic Lakes," June 2005), thawing permafrost may explain the shrinking or disappearance of hundreds of large Arctic lakes across western Siberia. The idea here is that rising air and soil temperatures thaw permafrost, allowing the lakes to drain away into the ground.

Neusiedler See, located in Austria and Hungary, has dried up many times over the millennia. As of 2005, it is again rapidly losing water, giving rise to the fear that it will be completely dry by 2010.

Some lakes disappear because of human development factors. The shrinking Aral Sea is described as being "murdered" by the diversion for irrigation of the rivers feeding it.

Extraterrestrial lakes

Io exhibits extraordinary variations in color and brightness as shown in this color-enhanced image.

Jupiter's small moon Io is volcanically active due to tidal stresses, and as a result sulfur deposits have accumulated on the surface. Some photographs taken during the Galileo mission appear to show lakes of liquid sulfur on the surface.

There are dark basaltic plains on the Moon, similar to lunar maria but smaller, that are called lacus (singular lacus, Latin for "lake") because they were thought by early astronomers to be lakes of water.

Photographs taken by the Cassini-Huygens spacecraft on July 24, 2006, give strong evidence for the existence of methane or ethene lakes on Saturn's largest moon, Titan.

Notable lakes

• The largest lake in the world by surface area is the Caspian Sea. With a surface area of 394,299 km² (152,240 mi²), it has a surface area greater than the next six largest lakes combined.
• The deepest lake is Lake Baikal in Siberia, with a bottom at 1,637 m (5,371 ft). Its mean depth is also the highest in the world (749 m)
  It is the world's largest freshwater lake by volume (23,000 km³), and the second longest (about 630 km from tip to tip).
• The longest freshwater lake is Lake Tanganyika, with a length of about 660 km (measured along the lake's center line).
  It is also the second deepest in the world (1,470 m) after lake Baikal.
• The world's oldest lake is Lake Baikal, followed by Lake Tanganyika (Tanzania).
• The world's highest lake is an unnamed pool on Ojos del Salado at .^[8] The Lhagba Pool in Tibet at comes second.^[9]
• The world's highest commercially navigable lake is Lake Titicaca in Peru and Bolivia at . It is also the largest freshwater (and second largest overall) lake in South America.
• The world's lowest lake is the Dead Sea, bordering Israel, Jordan at 418 m (1,371 ft) below sea level. It is also one of the lakes with highest salt concentration.
• Lake Superior is the largest freshwater lake by surface area (82,414 km²). It is also the third largest by water volume. However, Lake Huron and Lake Michigan form a single hydrological system with surface area 117,350 km², sometimes designated Lake Michigan-Huron. All these are part of the Great Lakes of North America.
• Lake Huron has the longest lake coastline in the world: about 2980 km, excluding the coastline of its many inner islands.
• The largest island in a freshwater lake is Manitoulin Island in Lake Huron, with a surface area of 2,766 km². Lake Manitou, located on Manitoulin Island, is the largest lake on an island in a freshwater lake.
• The largest lake located on an island is Nettilling Lake on Baffin Island.
• The largest lake in the world that drains naturally in two directions is Wollaston Lake.
• Lake Toba on the island of Sumatra is located in what is probably the largest resurgent caldera on Earth.
• The largest lake located completely within the boundaries of a single city is Lake Wanapitei in the city of Sudbury, Ontario, Canada.
  Before the current city boundaries came into effect in 2001, this status was held by Lake Ramsey, also in Sudbury.
• Lake Enriquillo in Dominican Republic is the only saltwater lake in the world inhabited by crocodiles.
• Lake of the Ozarks is one of the United States largest man made lakes, created by the Bagnell Dam ^[10]

Largest by continent

The largest lakes (surface area) by continent are:

• Africa - Lake Victoria, also the second largest freshwater lake on Earth. It is one of the Great Lakes of Africa.
• Antarctica - Lake Vostok (subglacial)
• Asia - Caspian Sea, also the largest on Earth. However, Europe-Asia border is conventionally drawn through it - the largest entirely in Asia is Lake Baikal.
• Australia - Lake Eyre
• Europe - Lake Ladoga, followed by Lake Onega, both located in northwestern Russia.
• North America - Lake Michigan-Huron
• South America - Lake Titicaca, which is also the highest navigable body of water on Earth at 3,821 m above sea level.

Note: Lake Maracaibo is considered by far the largest lake in South America. It, however, lies at sea level with a relatively wide opening to sea, so it is better described as a bay.

See also

• List of lakes
• List of world's largest lakes
• List of largest lakes of Western Europe
• List of world's deepest lakes
• Loch
• Lough
• Pond
• Limnology
• Lagoon
• Liman
• Slough (wetland)
• Mere (lake)
• Geography
• Tarn
• Deep lake water cooling
• Angling
• Lake monster

References

External links

• Lakes Database
• Lake Classification Systems
• UKLakes Database
• LV Lakes Database
• Midwest Lakes Policy Center
• Kashmir lakes
• Ponds and Lakes : definitions
• Some interesting Islands and Lakes

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