A lake is an inland body of relatively motionless water that usually has a river  or stream feeding into or draining out of it.

Lakes contain about 90% of all the surface water found on Earth (not including oceans). Lakes form when water finds its way into a basin. In order to continue existing, lakes must have a continual source of new water, otherwise they will eventually dry up.

Most lakes contain fresh water. However, in some cases, the water found in a lake can become salty, just like the ocean. This happens when a lake does not have a stream, either above ground or underground, draining water away from it. As water enters a lake, it carries minerals with it. As this water dissolves, it leaves the minerals behind.


Lakes differ to lagoons and estuaries due to the fact they are not connected to the ocean. A lake is also larger and deeper than other inland water bodies such as ponds.

The study of inland water bodies and ecosystems is called Limnology.

A lake usually contains freshwater but some can be saltwater.

  • Each lake has a larger catchment area (drainage basin, watershed) which is a large encompassing land area where surface water from rain, snow/ice melt, or rivers converges into the lower lying lake.
  • Water in most lakes flows in and out via rivers and streams. Lakes that only lose water by evaporation or underground seepage are called endorheic lakes.
  • The lowest lake in the world is the Dead Sea that borders Israel and Jordan. The surface level of which is 418 metres (1,371 ft) below sea level. It is also one of the saltiest lakes in the world.
  • The highest lake in the world is the crater lake of Ojos del Salado at 6,390 m (20,965 ft) above sea level. The mountain lake sits on the border of Chile and  Argentina.
  • The deepest lake in the world is Lake Baikal in Siberia, Russia. It is 1,637 m (5,371 ft) at its deepest point. Excluding the Caspian Sea it is the also the largest lake by volume in the world.
  • The Caspian Sea has characteristics of being both a sea and a lake. The saltwater sea used to be connected to the world’s oceans but became landlocked around 5.5 million years ago. It is often classed as a lake due to a lakes definition which would make it the largest lake in the world at 370,400 km² (143,244 mi²).
  • Located on the border of the United States and Canada are the Great Lakes of North America. They include 5 lakes: Michigan, Huran, Erie, Ontario, and Superior which together contain around 21% of the world’s freshwater supply. 
  • Finland has the nickname “Land of the Thousand Lakes” as there are over 187,000 lakes in the country.
  • There are many natural processes that can form lakes. The advancement and retreat of glaciers over millions of years can leave behind bowl-shaped depressions which fill. Lakes can also form by tectonic related changes of the landscape, or by landslides that cause water blockages. Crater lakes and calderas are formed in volcanic craters. Oxbow lakes are small, crescent-shaped lakes created by the meandering of rivers over time.
  • A lot of lakes today are artificially made to generate hydro-electric, for domestic water supply, for industrial or agricultural use, or for aesthetic and recreational purposes.

What’s the difference between a lake and a pond?

First, lakes are usually much deeper and wider than ponds. The water at the bottom is colder than the water at the top during the summer. In ponds, the water temperature near the top of the pond is about the same as the water temperature at the bottom of the pond. Plants grow prolifically in ponds. In lakes, they usually grow near the edges, but not in the middle.

How do lakes and ponds develop?

Lakes develop in many ways. As ancient glaciers slid down mountainslides, they sometimes caused huge piles of rocks to pile up. Lakes formed behind these rock piles as rain water collected. Volcanoes can also form lakes. Lava combining with cold water can cause huge explosions, leaving craters in the earth where a lake forms. Forest fires can also cause lakes. A marsh is a wet area filled with plants. As a forest fire rages through an area, it kills all the marsh plants, creating an open area for a lake.

Are lakes polluted?

Some lakes, especially those in mountain ranges, are quite clean. Others are very polluted. Pollution from fertilizers and soaps is a major problem. These fertilizers contain phosphates, which cause algae growth. When algae grow too much in lakes, they crowd out other plant life and animals.



lake origins








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