The East Kolkata Wetlands, spread over 12500 hectare on the eastern fringes of the city, one of the largest systems of wastewater agriculture in the world, comprise a large number of sewage fed water bodies are a complex of natural and human-made wetlands form a part of the extensive inter-distributary water networks of the Ganges where 250 million gallons of urban sewage flows into shallow ponds.
Wetland is located on the east Kolkata. It is the largest protected area in India and extends over 120 km, and consists pristine ecosystem. Like many other estuaries, the Wetland is home to several species of animals that reflect the concentration of different ecosystems created by variations in salinity season to season, year to year and from one point to another of the park.
The estuary is the largest in India and boasts, among other attractions, the largest fields. The marshes along the shores of the lake are filled by water seeping through the dunes, creating a refuge for life accustomed to fresh water when the salinity is too high.
The park consists of five ecosystems. These ecosystems are totally independent of each other, but complement each other. More specifically, and in accordance with the Ramsar International Convention , the term wetlands means the marshes and swamps, the peat bogs or the basins, natural or artificial, permanent or temporary, with water standing or running, sweet, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters.
The sites that have these characteristics and which are of international importance especially as habitat for waterfowl, may be included in the List of Wetlands of International Importance approved by the Convention.
They can therefore be considered to be wetlands the lakes, the bogs, the rivers and the estuaries, the ponds, the lakes , the fishing valleys, the shorelines with coastal marine waters. And also, between the man-made structures, the retention basins, the reservoirs restraint, the quarries of inert materials for fluvial activity, the channels, the saline and the tanks filled.
The marshes adjacent water courses, for example, create an effect sponge that collect water during floods slowing down the flow of water and reducing the risk of flooding then returning during the lean periods. They are also important reservoirs for groundwater. The rich and diverse wetland vegetation gives these environments, the ability to assimilate nutrients, namely nitrogen and potassium compounds, and the ability to create favorable conditions for the decomposition of microbial organic matter.
Half the wetlands have been lost, and most of the destruction occurred in the last 20 years. The main causes are the direct destruction, agriculture, encroachments and industry.