Lake

A lake is a large area filled with water, usually found on land. Unlike oceans, lakes are completely surrounded by dry ground. They are important because they give us fresh water to drink and help support plants and animals. Most lakes hold fresh water, but some contain salt water that can be even saltier than the ocean.

Lakes differ from smaller water areas like ponds because they are usually bigger and deeper. They can be found in many places, such as mountains, old volcanic craters, or areas where glaciers once were. Some lakes are fed by springs, rivers, or rain, while others have no outlet and stay filled only by rainfall.

People also create lakes called reservoirs for many useful reasons, like providing power, water for towns, or places for recreation. Even though lakes seem permanent, over very long times they can fill up with dirt or spill out and disappear.

Etymology, meaning, and usage of "lake"

The word lake has an interesting history. It comes from old languages like Middle English and Old English, and even older roots from Proto-Germanic and Proto-Indo-European. Other languages have similar words for lakes and small bodies of water, like Dutch and German.

It can be tricky to know exactly what makes a lake different from a pond. Scientists and experts don't all agree on a single definition. Some say lakes are just bigger versions of ponds, while others use the size of the water body to tell them apart. Sizes for what counts as a lake can vary, but generally, they are larger than ponds. Sometimes, places called "lakes" might mostly be dry land, only filling with water during heavy rains. In some areas, what people call a lake might actually be more like a pond, and vice versa, depending on where you are.

Distribution

Most lakes on Earth are filled with fresh water, and they are mainly found in the Northern Hemisphere at higher latitudes. Canada has around 31,752 lakes that are bigger than 3 square kilometres, and it's believed to have at least 2 million lakes in total. Finland has about 168,000 lakes that are 500 square metres or larger.

Lakes often have rivers or streams that flow out of them, helping to keep their water level steady by draining extra water. Some lakes don't have a natural outflow and lose water only through evaporation or seeping underground. These are called endorheic lakes.

Many lakes are made by people for reasons such as generating power, making places look beautiful, giving people places to play and relax, helping with farming, or providing clean water for homes.

The exact number of lakes on Earth is not known because many are very small and don't show up on maps or satellite pictures. However, studies show that there are many more small ponds than large lakes. Even though there are lots of small ponds, almost all the water in lakes is stored in just a few very large lakes. This is because a lake's volume grows faster than its area.

There are also lakes on Saturn's moon Titan, and they look much like Earth's lakes. Mars used to have lakes on its surface, but they are now dry lake beds.

Types

In 1957, a scientist named G. Evelyn Hutchinson wrote a big book about lakes. He talked about how lakes are formed and sorted them into different groups. There are 11 main types of lakes, and each type has many smaller kinds.

Tectonic lakes

Tectonic lakes are made when the Earth's surface moves and shifts. This can happen when the ground cracks, folds, or tilts. Some very large lakes, like Lake Baikal, were formed this way. Other lakes, such as the Great Salt Lake, are in places where water cannot flow out easily because of these ground movements.

Volcanic lakes

Main article: Volcanogenic lake

Volcanic lakes are formed by volcanoes. They can be in old volcano craters or in big valleys made by volcanic eruptions. An example is Crater Lake in Oregon, which formed in the crater of an ancient volcano.

Glacial lakes

Main article: Glacial lake

Glacial lakes are made by glaciers, huge blocks of ice that move and shape the land. These lakes are very common in places like northern Europe and North America. Some glacial lakes are next to ice, while others are in valleys carved by glaciers.

Fluvial lakes

Fluvial lakes are made by rivers. One common type is called an oxbow lake, which forms when a river changes its path and leaves a curved lake behind.

Solution lakes

Solution lakes are formed when rainwater dissolves parts of the ground, creating holes that fill with water. These are common in places with limestone rock, like Florida.

Landslide lakes

Landslide lakes happen when a landslide blocks a river, creating a lake. These lakes can be big but often disappear after a while.

Aeolian lakes

Aeolian lakes are made by wind. They are usually found in dry places where wind moves sand and creates barriers that trap water.

Shoreline lakes

Shoreline lakes are formed near coastlines when sand or other materials block off a piece of water from the ocean.

Organic lakes

Organic lakes are made by plants and animals, like those created by beavers building dams. These lakes are usually small.

Artificial lakes

See also: Reservoir, water storage, and retention basin

Artificial lakes are made by people. They are often created by building dams to hold back river water. These lakes can be used for drinking water, electricity, or just for beauty in parks.

Meteorite (extraterrestrial impact) lakes

Main article: Impact crater lake

Meteorite lakes are formed when space rocks crash into Earth and create craters that fill with water. Examples include Lonar Lake in India and Lake El'gygytgyn in Siberia.

Other classification methods

Lakes can be grouped in many ways, such as by how warm or cold the water is, how much oxygen it has, and how its size changes with the seasons. People in different places may use different names for lakes based on these features or on what the lake looks like.

One important way to group lakes is by how the water’s temperature changes with depth. Colder, heavier water usually sits at the bottom of a lake, while warmer water sits on top. This pattern can change with the seasons or depending on the lake. Scientists study these patterns to understand how plants and animals live in the lake.

Lakes can also be grouped by how much their water level changes through the year. Some lakes only fill with water for part of the year and then dry up, while others hold water all year long. Different places may have special names for these kinds of lakes.

Lakes can also be grouped by the chemistry of their water. Some lakes have water that is more acidic, meaning it has a lower pH level, which can affect the plants and animals that live there. Other lakes may have lots of salt in them, making them very different from regular freshwater lakes.

Paleolakes

A paleolake (also palaeolake) is a lake that existed a long time ago when water conditions were different. We can find evidence of these old lakes by looking at special shapes on the land, like old shorelines, and by studying the dirt and tiny remains left behind.

There are two types of paleolakes:

• A former lake is a paleolake that no longer exists. These lakes have dried up, sometimes because of nature or because people changed the area. One example is Owens Lake in California, United States.
• A shrunken lake is a paleolake that still exists but is much smaller now. An example is Lake Agassiz, which once covered a large part of central North America. Today, parts of it remain as Lake Winnipeg and Lake Winnipegosis.

Paleolakes help scientists understand how Earth’s surface has changed over time. They also sometimes contain important resources like oil and natural gas.

Characteristics

Lakes have many features, such as their drainage basin (or catchment area), the nutrients they contain, and their pH levels. The level of a lake changes based on how much water flows in compared to how much flows out. Water can come from rain, streams, and groundwater, while it leaves through evaporation and human use.

Lakes can be grouped by how many nutrients they have. Some lakes have few nutrients and clear water, while others have lots of nutrients, which can cause lots of plant growth and algae. These changes often happen because of human activities, like using fertilizers.

Lakes can also form layers of water with different temperatures, called thermoclines. In colder climates, these layers can mix, bringing fresh oxygen to the bottom. In tropical lakes, the layers usually don’t mix, which can sometimes cause dangerous gas releases. The bottom of a lake, called the lake bed, is made of different materials like sand, silt, and decaying plants or animals, which affect the life in the lake.

Limnology

Limnology is the study of lakes and other water bodies on land and the life around them. Lakes have three main zones: the littoral zone, which is the area near the shore; the photic or open-water zone, where there is plenty of sunlight; and the deep-water profundal or benthic zone, where little sunlight reaches. How deep the light can go depends on how clear the water is, which is affected by tiny bits of material floating in it.

The clarity of the water can be checked using a Secchi disk, a special disk that helps measure how clear the water is. Lakes can also help control the temperature around them because water can hold a lot of heat.

Lakes have different zones where plants and tiny organisms live. Some algae grow on mud, rocks, sand, plants, or even animals. These tiny plants help make the lake a home for many creatures.

Disappearance

Lakes can change over time. They may fill up with dirt and plants and turn into wetlands like swamps or marshes. Plants such as reeds help this process by breaking down and forming peat soil. Sometimes, marshes can burn and turn back into shallow lakes. This back-and-forth happens naturally but has been changed by humans not allowing wildfires.

Some lakes only appear for part of the year. These are called intermittent, ephemeral, or seasonal lakes. They can be found in special landscapes where rain fills up dry lake beds. For example, Lake Cerknica in Slovenia or Lag Prau Pulte in Graubünden appear and disappear with the seasons. Even very dry places like Death Valley can have temporary lakes after heavy rains.

Lakes can also disappear quickly due to natural changes. For instance, Lake Beloye in Nizhny Novgorod Oblast, Russia, vanished in minutes when the soil beneath it shifted.

Some lakes shrink because of human activities and climate change. The Aral Sea has become much smaller because rivers that fed it were used for farming.

Extraterrestrial lakes

Only one place besides Earth is known to have big lakes: Saturn's largest moon, Titan. Pictures and special tests by the Cassini–Huygens spacecraft show a liquid called ethane on its surface, mixed with another liquid called methane. The biggest lake on Titan is Kraken Mare, which is about five times larger than Lake Superior and almost as big as all five Great Lakes in North America together. The second biggest lake on Titan, Ligeia Mare, is almost twice the size of Lake Superior.

Jupiter's moon Io has lots of volcanic activity, and some pictures from the Galileo mission seem to show lakes of liquid sulfur on its surface.

The planet Mars has one known underground lake near its south pole. Even though Mars is too cold and has too little air to keep water on its surface forever, signs on the planet show that long ago, lakes might have existed there.

There are dark areas on the Moon that look like small seas. These are called lacus (singular lacus), and early space scientists thought they might be lakes of water.

Notable lakes on Earth

See also: List of lakes

• The largest lake by surface area is Caspian Sea, which despite its name is considered a lake from the point of view of geography. Its surface area is 143,000 sq. mi./371,000 km².
  • The second largest lake by surface area, and the largest freshwater lake by surface area, is Lake Michigan-Huron, which is hydrologically a single lake. Its surface area is 45,300 sq. mi./117,400 km². For those who consider Lake Michigan-Huron to be separate lakes, and Caspian Sea to be a sea, Lake Superior would be the largest lake at 82,100 km² (31,700 square miles)
• Lake Baikal is the deepest lake in the world, located in Siberia, with a bottom at 1,637 metres (5,371 ft). Its mean depth is also the greatest in the world (749 metres (2,457 ft)). It is also the world's largest freshwater lake by volume (23,600 cubic kilometres (5,700 cu mi), but much smaller than the Caspian Sea at 78,200 cubic kilometres (18,800 cu mi)), and the second longest (about 630 kilometres (390 mi) from tip to tip).
• The world's oldest lake is Lake Baikal, followed by Lake Tanganyika in Tanzania. Lake Maracaibo is considered by some to be the second-oldest lake on Earth, but since it lies at sea level and nowadays is a contiguous body of water with the sea, others consider that it has turned into a small bay.
• The longest lake is Lake Tanganyika, with a length of about 660 kilometres (410 mi) (measured along the lake's center line).
  It is also the third largest by volume, the second oldest, and the second deepest (1,470 metres (4,820 ft)) in the world, after Lake Baikal.
• The world's highest lake, if size is not a criterion, may be the crater lake of Ojos del Salado, at 6,390 metres (20,965 ft).
  • The highest large (greater than 250 square kilometres or 97 square miles) lake in the world is the 290-square-kilometre (110 sq mi)^{[citation needed]} Pumoyong Tso (Pumuoyong Tso^{[citation needed]}), in the Tibet Autonomous Region of China, at 28°34′N 90°24′E / 28.567°N 90.400°E / 28.567; 90.400, 5,018 metres (16,463 ft) above sea level.
  • The world's highest commercially navigable lake is Lake Titicaca in Peru and Bolivia at 3,812 m (12,507 ft). It is also the largest lake in South America.
• The world's lowest lake is the Dead Sea, bordered by Jordan to the east and Israel and Palestine to the west, at 418 metres (1,371 ft) below sea level. It is also one of the lakes with highest salt concentration.
• Lake Michigan–Huron has the longest lake coastline in the world: about 5,250 kilometres (3,260 mi), excluding the coastline of its many inner islands. Even if it is considered two lakes, Lake Huron alone would still have the longest coastline in the world at 2,980 kilometres (1,850 mi).
• The largest island in a lake is Manitoulin Island in Lake Michigan-Huron, with a surface area of 2,766 square kilometres (1,068 sq mi). Lake Manitou, on Manitoulin Island, is the largest lake on an island in a lake.
• The largest lake on an island is Nettilling Lake on Baffin Island, with an area of 5,542 square kilometres (2,140 sq mi) and a maximum length of 123 kilometres (76 mi).
• The largest lake in the world that drains naturally in two directions is Wollaston Lake.
• Lake Toba on the island of Sumatra is in what is probably the largest resurgent caldera on Earth.
• The largest lake 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 Bernard, Ontario, Canada, claims to be the largest lake in the world with no islands.
• Lake Saimaa in both South Savo and South Karelia, Finland, forms the much larger Saimaa basin, which have more shorelines per unit of area than anywhere else in the world, with the total length being nearly 15,000 kilometres (9,300 mi).
• The largest lake in one country is Lake Michigan, in the United States. However, it is sometimes considered part of Lake Michigan-Huron, making the record go to Great Bear Lake, Northwest Territories, in Canada, the largest lake within one jurisdiction.
• The largest lake on an island in a lake on an island is Crater Lake on Vulcano Island in Lake Taal on the island of Luzon, The Philippines.
• The northernmost named lake on Earth is Upper Dumbell Lake in the Qikiqtaaluk Region of Nunavut, Canada at a latitude of 82°28'N. It is 5.2 kilometres (3.2 mi) southwest of Alert, the northernmost settlement in the world. There are also several small lakes north of Upper Dumbell Lake, but they are all unnamed and only appear on very detailed maps.
• There are only 20 ancient lakes – those over a million years old

Largest by continent

The largest lakes (surface area) by continent are:

• Australia – Lake Eyre (salt lake)
• Africa – Lake Victoria, also the third-largest freshwater lake on Earth. It is one of the Great Lakes of Africa.
• Antarctica – Lake Vostok (subglacial)
• Asia – Lake Baikal (if the Caspian Sea is considered a lake, it is the largest in Eurasia, but is divided between the two geographic continents)
• Oceania – Lake Eyre when filled; the largest permanent (and freshwater) lake in Oceania is Lake Taupō.
• Europe – Lake Ladoga, followed by Lake Onega, both in northwestern Russia.
• North America – Lake Michigan–Huron, which is hydrologically a single lake. However, lakes Huron and Michigan are usually considered separate lakes, in which case Lake Superior would be the largest.
• South America – Lake Titicaca, which is also the highest navigable body of water on Earth at 3,812 metres (12,507 ft) above sea level. (The much larger – and older – Lake Maracaibo is perceived by some to no longer be genuinely a lake, but a lagoon.^{[citation needed]})