Lakes are expanses of water, generally calm, which fill up hollows of the Earth. Their appearance depends on the different ways in which they began. The water of a lake can be fed by underground streams or from a river which enters into the lake as intake and cannot escape as outtake.
For instance, lakes can fill the craters of extinct volcanoes.

Form of Lakes

The form of a lake depends on its origin.

Volcanic lakes are small and have the circular shape of craters.

Glacial lakes which are formed in high regions are have circular shape.
Those which have a thin, long shape are found in valleys.

Coastal lakes are parallel to the coast and are formed when the sand holds back the water of a river as it flows towards the sea.

What How Why

How fast can a dog run?

A Greyhound can run at a speed of 64km per hour, a Weimaraner , once used for hunting wolves and wild boar, can reach speed of up to 56 km per hour in a chase. Many breeds of dog which were once bred for hunting are now more common as pets than hunting Dogs.

Artificial Lakes

Large quantities of water can be collected in an artificial lake.
The water can be then converted to power hydroelectric stations, irrigation plants and water distribution systems in built-up areas.