• Lakes are formed in hollows of the land surface where water accumulates
• Lakes vary in size, shape, depth, and mode of formation
• Tiny lakes are no bigger than ponds or pools while large ones are extensive like seas, e.g. Caspian Sea
• Lakes are temporary features of the Earth’s crust and can be eliminated by draining and silting up
• Most lakes in the world are fresh water lakes fed by rivers
• In regions where evaporation is greater than precipitation and few streams fill up the lake, saline water lakes form, such as Dead Sea and Great Salt Lake of Utah.

Lakes formed by earth movement

• Tectonic lakes
  • Tectonic depressions occur due to warping, bending & fracturing of earth crust
  • Examples: Lake Titicaca (at Andes) – highest lake of the world, Caspian Sea (largest lake of the world & 5 times larger than its nearest rival i.e. Lake Superior)
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• Rift Valley Lakes
  • Formed due to faulting, creating a deep, narrow & elongated trough between two parallel faults
  • Floors are often below sea level and water collects in these troughs
  • Examples: Lake Tanganyika (world’s deepest lake) & Dead Sea (world’s lowest lake)
  • 

Lakes formed by Glaciation

• Cirque Lakes/Tarns:
  • Formed in circular hollows left by glaciers in the heads of valleys
  • Over deepened floors may be filled with water to form cirque lakes
  • Ribbon lakes are those that occupy long and deep glacial troughs down the valley
  • 
• Kettle Lakes:
  • Depressions in the outwash plain left by the melting of masses of stagnant ice
  • Irregular in shape and never of great size or depth
  • 
• Rock Hollow Lakes:
  • Formed by ice scouring when valley glaciers or ice sheets scoop out hollows on the rock surface
  • Enclosed within a rock hollow
  • Abundant in Finland
• Lakes formed due to Moraine damming of Valleys:
  • Valley glaciers deposit moraine debris across a valley, damming it and forming lakes
  • Lateral and terminal moraines can both dam valleys
• Lakes formed due to deposition of glacial drifts:
  • Form in depressions in glaciated lowlands with a predominant drumlin landscape
  • Poor drainage leads to waterlogged depressions and small lakes form.

Lakes formed by volcanic activity

• Crater & Caldera Lakes:
  • Formed during a volcanic explosion when the top of the cone is blown off, leaving a natural hollow called a crater which may be enlarged into a caldera.
  • In dormant and extinct volcanoes, rain falls into the crater or caldera with no superficial outlet, forming a crater or caldera lake.
  • 
• Lava Blocked Lakes:
  • In volcanic regions, a stream of lava may flow across a valley which solidifies and dams the river, leading to the formation of lava blocked lakes.
• Lakes formed due to subsidence of volcanic land surface:
  • The crust of hollow lava flow may collapse, leaving behind a wide and hollow depression in which a lake may form.

Lakes formed by Erosion

• Karst lakes:
  • Rainwater dissolves limestone to form solution hollows, which may become clogged with debris and form lakes.
  • Collapse of limestone roofs of underground caverns may expose long, narrow lakes that were once underground.
  • Polje, large depressions without an outlet, may contain lakes.
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• Wind deflated lakes:
  • Winds in deserts create deep hollows that reach the water table and form small, shallow lakes.
  • Excessive evaporation can cause these lakes to become salt lakes or Playas.

Lakes formed by Deposition

• Lakes formed due to river deposits:
  • A river may shorten its course during a flood by cutting its meandering loops leaving behind a horseshoe-shaped channel called an ox-bow lake.
• Lakes formed due to marine deposits:
  • The action of wind & waves may isolate lagoons along the coasts, enclosed by a narrow spit of land known as lagoon lakes. 
  • Lagoons are a shallow body of water separated from a larger body of water by barrier islands or reefs. 
  • In East Germany & Poland, lagoons are called Haffs.
• Lakes formed due to landslides, screes & avalanches:
  • Landslides or screes may block valleys so that rivers are dammed, leading to the formation of temporary lakes. 
  • Lakes formed by these processes are also known as barrier lakes. 
  • Such lakes are short-lived because the loose fragments that pile up across the valleys will soon rupture under pressure and give way to water. 
  • When they suddenly give way, the dammed water rushes down causing floods.

Lakes formed by Human & Biological activities

• Man-made lakes:
  • Concrete dams are built across river valleys to form reservoirs.
• Lakes made by animals:
  • Beavers construct dams across rivers with timber, mud, and soil, which are quite permanent and modify the natural environment.
• Other types of man-made lakes:
  • Ornamental lakes are especially made to attract tourists.
  • Inland fishing lakes are developed for inland fish culture.