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Good practice Imported

East Kolkata Wetlands: Sewage-Fed Fisheries Treating Kolkata's Wastewater

India · Kolkata · See the India profile

Evidence: Observational / pre–post Top 33% 53/100 · Ask Evidence Copilot about this practice

A 125 km² Ramsar wetland east of Kolkata where cooperative fisheries treat ~910 million litres of the city's sewage daily, supply about a third of its fish and sustain ~50,000 livelihoods — though encroachment has shrunk it by over a third since the 1990s.

~910 million litres
Sewage treated daily
~1/3
Share of Kolkata's fish demand supplied
~50,000
Agro-workers employed
~65 km2 to 41 km2
Protected area shrinkage (over ~3 decades)
East Kolkata Wetlands: Sewage-Fed Fisheries Treating Kolkata's Wastewater

Details

Maturity
Established
Promoter
East Kolkata Wetlands Management Authority
Period
1992-present
Keywords
wastewater treatment, aquaculture, urban wetlands

Context

East Kolkata Wetlands is a roughly 125 km2 mosaic of sewage-fed fisheries, paddy fields and garbage farms east of Kolkata; a 1992 Calcutta High Court ruling blocked development and affirmed it should be preserved, and the site was Ramsar-designated in 2002.

Activities

Farmers channel the city's raw sewage through canals into fish ponds, where solar-driven algal and bacterial processes strip organic load and nutrients before reuse for irrigation and pisciculture, described as the world's largest operating system of wastewater-fed aquaculture.

Results

The system treats an estimated 910 million litres of Kolkata's sewage per day, supplies roughly a third of the city's fish demand, and employs on the order of 50,000 agro-workers.

Conclusions

Independent studies report the protected area has shrunk from about 65 km2 to 41 km2 over roughly three decades due to illegal landfilling, and peer-reviewed sampling has found elevated heavy-metal levels in wetland fish, water and sediment, raising food-safety questions.

Implementation
Indicative cost
Low (< €50k)
Time to results
Long (> 3 years)
Staffing & skills
East Kolkata Wetlands Management Authority, cooperative fisheries and farmers

Conditions for success

  • 1992 court ruling and 2006 conservation act establishing legal protection
  • solar-driven natural treatment process requiring no mechanical plant

Common failure modes

  • over a third of the protected area lost to illegal landfilling and land-use conversion
  • elevated heavy-metal levels found in fish, water and sediment

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Data sources

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