A view of the Calcutta wetlands

Wetlands are low-lying areas that get filled with water due to various reasons. The amount of water in them varies with their type, their location, the weather and the time of year. There are many kinds of wetlands in the world—some are dark and dangerous--like bogs—and some, like the marshes, billabongs and estuarine wetlands, are green and serene places filled with shallow, water-bodies.

Bogs are the most common form of wetland areas in Canada and most places in the Northern Hemisphere that used to be glacier beds. Bogs are known for their high water tables, acidic vegetation and peat accumulation. Bogs have no real inflows or outflows of water and are stagnant pools that have, over the centuries, been covered with a layer of floating vegetation. The spongy sphagnum moss, peat accumulation and the vegetation cover make Bogs look like solid ground and are primarily responsible for their being dangerous.

Marshes and Swamps are lowland areas filled with reeds.

Billabongs are old river-beds abandoned when a river changes its course. During rains or floods, these areas fill with water and become a haven for wildlife.

Estuarine wetlands and mangrove marshes occur at the point where a river begins to merge into the sea. These areas are filled with brackish water that is a mixture of fresh river water and salt sea water. The water in estuarine wetlands rises and falls according to the tides.

Some wetlands like the extensive Calcutta Wetlands have developed in their own special way. These large tracts of water-bodies called “Bheris” have developed between the distributories of two rivers—the Hoogly and the Bidyadhari—as they meandered their way into the Bay of Bengal.

These marshy areas used to be a tidal channel and acted like spill-basins or places where the extra tidal water was collected. Gradually, the Calcutta Wetlands changed character because embankments were built around them for agricultural and piscicultural (fish cultivation) purposes.

These wetlands are used to treat the city’s sewage and a big part of the "bheris" or water-bodies have been reclaimed for construction.


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