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 also have words for lakes and small bodies of water, like Dutch and German.

It can be hard to know what makes a lake different from a pond. Scientists don’t all agree on one definition. Some say lakes are just bigger ponds, while others look at the size to tell them apart. Generally, lakes are larger than ponds. Sometimes places called “lakes” might be mostly dry land and only fill with water after heavy rains. In some areas, what people call a lake might really be a pond, and vice versa, depending on where you are.

Distribution

Most lakes on Earth have fresh water. They are mainly found in the Northern Hemisphere. Canada has many lakes, and Finland also has a lot.

Lakes often have rivers or streams that flow out of them. 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 making places look beautiful, giving people places to play and relax, or providing clean water for homes.

The exact number of lakes on Earth is not known because many are very small. There are also lakes on Saturn's moon Titan. Mars used to have lakes, but they are now dry.

Types

In 1957, a scientist named G. Evelyn Hutchinson wrote a book about lakes. He talked about how lakes are formed and sorted them into groups. There are 11 main types of lakes.

Tectonic lakes

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

Volcanic lakes

Main article: Volcanogenic lake

Volcanic lakes are formed by volcanoes. They can be in old volcano craters or in valleys made by 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 common in places like northern Europe and North America. Some 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. 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, 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 long 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 and the nutrients they contain. 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. These changes often happen because of human activities.

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

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.

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.

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 has big lakes: Saturn's largest moon, Titan. Pictures and special tests from 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 is a lake even though it is called a sea.
  • The second largest lake by surface area, and the largest freshwater lake by surface area, is Lake Michigan-Huron. 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.
• Lake Baikal is the deepest lake in the world, located in Siberia. It is also the world's largest freshwater lake by volume, and the second longest lake in the world.
• The world's oldest lake is Lake Baikal, followed by Lake Tanganyika in Tanzania.
• The longest lake is Lake Tanganyika.
  It is also the third largest by volume, the second oldest, and the second deepest 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.
  • The highest large lake in the world is Pumoyong Tso in the Tibet Autonomous Region of China.
  • The world's highest commercially navigable lake is Lake Titicaca in Peru and Bolivia. 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. It is also one of the lakes with highest salt concentration.
• Lake Michigan–Huron has the longest lake coastline in the world.
• The largest island in a lake is Manitoulin Island in Lake Michigan-Huron.
• The largest lake 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 in a very large caldera.
• The largest lake completely within the boundaries of a single city is Lake Wanapitei in the city of Sudbury, Ontario, Canada.
• 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, has more shorelines per unit of area than anywhere else in the world.
• 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 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. There are also several small lakes north of Upper Dumbell Lake, but they are all unnamed.

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. 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.