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EveryFish

River or lake, India

East Kolkata Wetlands

Sewage-fed fish ponds on Kolkata's eastern edge, a Ramsar site where the city's waste water grows carps and tilapia.

On the eastern edge of Kolkata lie the East Kolkata Wetlands, about 12,500 hectares of shallow fish ponds called bheris, farms and vegetable plots. For about a century, the city's sewage has flowed into these ponds, where sunlight, algae and bacteria break it down and the nutrients grow plankton that feeds fish. The system was listed as a Ramsar wetland of international importance in 2002.

How the bheris work

Waste water is let into the ponds and left to settle for some weeks, while algae grow and bacteria break down the waste. Farmers then stock fingerlings of rohu, catla, mrigal, silver carp and tilapia, which feed on the plankton. The cleaned water flows on to irrigate rice and vegetables. The engineer Dhrubajyoti Ghosh studied and championed the system from the 1980s, and it is often cited as one of the largest working examples of using waste water to grow food.

A wetland under pressure

The wetlands supply fish to Kolkata's markets and support many thousands of fishers and farm workers. They also save the city the cost of a large sewage plant. But the city has spread east, and the growth of Salt Lake, New Town and the eastern bypass has taken land. Some ponds have been filled, and industrial waste in the sewage raises concerns about heavy metals in fish. Courts and the state wetlands authority restrict building inside the protected area.

Fish of East Kolkata Wetlands

RohuStocked in the sewage-fed bherisNile tilapiaHardy fish common in the wetlands

Still to be written: Catla, Cirrhinus mrigala, Silver carp.

Photo credits on this page

The small pictures above come from Wikimedia Commons under free licences. Some are cropped to fit.

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