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Lake
Most lakes contain fresh
water, but some inland lakes are salty. Examples of salty lakes include the Great Salt Lake of Utah. Very salty lakes that dry up from time to time, called playa lakes, are found in places where the lakes have no outlet, and where the rivers that drain into them cross beds of salty rock.
Lake Superior covers 82,100
sq km and is the largest lake in the world in terms of area. Lake Baikal in Siberia has the largest volume
of water, some 23,000 cu km.
The land with the largest density
of lakes may be Finland, which
has tens of thousands of small lakes. The country with the largest number of lakes may be Canada because it is the largest country to be glaciated.
Lakes are not formed by rivers, and they do not last long compared to the history of the Earth. Most have a life of just a few hundred
or a few thousand years. After
that they become filled in with
the sediment brought to them by inflowing rivers.
The upper parts of lakes are good for fish and other water life because there is light, oxygen, heat, and nourishment brought
Some plants are adapted to float and can colonize deeper water.
Some fish are adapted to feed in the mud of the lake bed.
in by rivers. But deeper waters have little light and
less nourishment or oxygen, so the number of species is often small.
Lakes are not
good at cleaning
themselves. If they
become polluted
by sewage or
waste from
factories, the life
in them may be
threatened. Lake
Erie, for example, is officially designated as a dead lake due to pollution.
Lakes are very important sources of water for cities, factories,
and irrigation. Where there are insufficient natural lakes, people often create them by building dams. An artificial lake is
called a reservoir.
Lakes are also often used
for transportation, connecting cities that lie on opposite sides of the lake.
 Lake—This image from space shows Lake Titicaca, Bolivia and Peru, the largest lake in South America.
Little light reaches the lake floor.
On unexposed shores plants thrive in the sunlit shallows. It is these lake edges that have the highest density of animals and plants.
 Lake—Lakes support a wide range of life, from plants, fish, and insects, to amphibians and birds like herons.
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