The wetlands system processes about 60 percent of Kolkata’s sewage free of charge, saving the city over $64 million a year.
Farms in the wetlands provide about 150 tons of vegetables daily, 10,500 tons of fish annually and employ tens of thousands of people.
For Kolkata, on the vast delta where the Ganges River meets the Indian Ocean, the wetlands also provide flood defenses for a city facing rising sea levels due to climate change.
About 95 percent of the wetlands are in private hands.
As land prices surge, environment officials say they have pleaded with people not to fill in the fish ponds to create new building space.
But residents say village councils are being bribed by land-hungry developers.