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A lake is a low-lying part of the Earth's surface in which rainwater, surface water run-off, outflow from a river, and water from other sources accumulates. There is a great variety of lakes on Earth: there are freshwater lakes and saltwater lakes, ranging in size from small fish-ponds to huge waterbodies such as Lake Superior in USA which is the world's largest freshwater lake. The Caspian Sea in Europe and the Sambhar lake in Rajasthan are examples of saltwater lakes. India has a large number of lakes spread all over the country, from Kashmir to Kerala and from Rajasthan to Assam. Among the better-known fresh water lakes in India are the Dal lake in Srinagar and the Nainital lake. Whether natural or manmade, all lakes are major sources of water. Lakes are homes to a large variety of aquatic life, with one notable exception: the Dead Sea, a saltwater lake in Israel does not have any form of life. There is too much salt in its water to sustain life.

The deepest lake is Lake Baikal in Siberia, Russia. The deepest point of the lake is known as the Olkhon Crevice; it has a depth of 5,370 feet.
The largest saline lake is the Caspian Sea, spread over parts of Iran, Russia, Turkmenistan, Azerbaijan, and Kazakhstan with a surface area of 1 43 560 square miles and an estimated volume of 21 500 cubic miles
The most threatened lake in terms of size is the Aral Sea, which has shrunk due to extraction of water for irrigation.

Almost half of the world's lakes are degraded, depleted, and contaminated mainly by human activities. The main causes are inflow of domestic sewage, agricultural run-off, discharge of industrial effluents, over-fishing, introduction of exotic species and habitat degradation from population growth, expansion of cities.
As more water is withdrawn for human use and more of it is returned to lakes and rivers badly polluted there is less available to maintain vital freshwater ecosystems

Some Indian lakes

Keoladeo National Park
This is an important habitat for waterfowl. It is the only wintering site in India for the central and western Asian population of Siberian cranes, a highly endangered species. The population of Siberian Cranes has decreased in the last two decades. In a programme now underway, reared Siberian crane chicks are being brought to Keoladeo from USA and Siberia. Loktak Lake. The measures undertaken for the conservation of Loktak Lake so far, include afforestation of indigenous species including fruit trees; control of silt; catchment area treatment; removal of floating lands locally called phumdis in some pockets of the lake; and generating awareness about the values and functions of the wetland. Several measures have been adopted to control the prolific growth of phumdis and water hyacinth. Weevils have been introduced for biological control of water hyacinth.

Harike Lake
This wetland sustains a large number of waterfowl. Demarcation of the wetland has been attempted, and fencing has been carried out of some ponds. Afforestation of catchment area has been carried out in some critical areas to control siltation. One of the major problems faced by this wetland is the prolific growth of water hyacinth

Wular Lake
This wetland is the source of drinking water for Srinagar, and also acts as an absorption basin for floodwater. It is an important waterfowl habitat. However, Wular Lake is subject to heavy siltation due to loss of vegetal cover in the surrounding area.

Sambhar Lake
Located in the arid zone of Rajasthan, the Sambhar Lake is one of the largest inland saline lakes in India. This wetland is one of the most important wintering areas for flamingoes and pelicans. Salt extraction is one of the major activities in the wetland.

The Bhoj Wetland in Bhopal, Madhya Pradesh
It consists of two man-made lakes (upper and lower lakes). The upper lake was created in the 11th century by constructing an earthen dam across the Kolans river and the lower lake was constructed nearly two centuries ago.

The wetland supports a wide variety of flora and fauna. Diverse flora provide ideal habitat for a large number of avifauna. Biotic interaction and natural selection have led to the development of a characteristic relationship between vegetation and the avifauna.

Deepor Beel
This is a permanent freshwater lake, in a former channel of the Brahmaputra river, south-west of Guwahati city. It is a large natural wetland having great biological and environmental importance and is also the only major storm water storage basin for Guwahati. The beel is endowed with rich floral and faunal diversity. In addition to a huge congregation of residential water birds, the Deepor ecosystem harbours a large number of migratory waterfowl each year. It is now threatened with large scale encroachment, brick making factory and soil cutting within the beel ecosystem, and construction of railway line along the southern boundary of the beel.

The Hussain Sagar Lake
This is one of the largest man-made lakes in Asia, located in the heart of Hyderabad, contributing to its immense beauty. It is a sprawling artificial lake that holds water perennially. It was built during the reign of Ibrahim Qutub Shah in 1562, on a tributary of the river Musi.

The Tso Morari Lake
This is one of the largest in the Ladakh region and is almost like an inland sea. Situated at an elevation of about 4,900m, it is about 22km long, with a width varying from 5 to 7km and a depth of more than 30 m at the deepest point.

The lake is probably a leftover from the Ice Age, formed by the melt waters of the ice masses left behind by the retreating glaciers. The waters from the surrounding areas drained into the lake. The huge amounts of water present in the beginning evaporated very fast in the desert-like atmosphere and what was fresh water became brackish and finally salty, unfit for human consumption.

One of the most spectacular lakes in Ladakh is the Pangong Tso, which lies across the Changla Pass from Leh. At an altitude of almost 4,500 metres, the Pangong Tso is only 8 km wide at its broadest point, but is an amazing 134km long. The Pangong is considered to be the longest lake in Ladakh. It is a saltwater lake formed in much the same way as the Tso Morari lake during the Ice Age.


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