When Mumbai came to a standstill after days of relentless rain this week, the images were all too familiar — flooded roads, stranded commuters, delayed trains, and neighbourhoods struggling to stay afloat.
Across India, intense cloudbursts and short bursts of heavy rainfall are becoming more frequent, exposing the limits of concrete drains and ageing urban infrastructure.
But hundreds of kilometres away, Kolkata offers a different lesson.
On the eastern edge of the city lies a 12,500-hectare stretch of wetlands that quietly absorbs excess rainwater, naturally treats sewage, supports thousands of livelihoods, and protects the city from flooding.
Known as the East Kolkata Wetlands (EKW), this remarkable ecosystem proves that sometimes, the smartest climate solution isn’t built with cement — it’s already growing in nature.
Nature’s sponge for a growing city
Often called the “natural kidneys” of Kolkata, the East Kolkata Wetlands work much like the human body. Just as kidneys filter waste from our blood, these wetlands filter wastewater before it returns to the environment.
Recognised as a Ramsar Site, or a Wetland of International Importance, in 2002, the EKW is also regarded as the world’s largest natural resource recovery ecosystem. Every day, a large portion of Kolkata’s sewage flows into the wetlands, where sunlight, algae, aquatic plants, and naturally occurring microorganisms clean the water without the need for energy-intensive treatment plants.
pread across 12,500 hectares, Kolkata’s wetlands show how protecting ecosystems can provide climate solutions while supporting communities and livelihoods. Photograph: (LBB)
The nutrient-rich water is then reused in fish ponds and agriculture, creating a circular economy that has sustained local communities for generations.
A climate solution hidden in plain sight
While wastewater treatment is one of its most well-known roles, the wetlands perform another critical function during the monsoon — they store excess rainwater.
Instead of allowing heavy rainfall to overwhelm city drains, the wetlands act like a giant sponge. They slow down runoff, temporarily hold floodwater, and gradually release it, reducing waterlogging across Kolkata.
Scientists describe this as a nature-based solution, where healthy ecosystems provide services that expensive grey infrastructure often struggles to match.
As climate change brings more intense rainfall events, these natural flood buffers are becoming increasingly valuable.
Supporting livelihoods while protecting the environment
The East Kolkata Wetlands are also one of the few places in the world where conservation and livelihoods go hand in hand.
More than 250 sewage-fed fisheries, along with vegetable farms and paddy fields, depend on this ecosystem. Wastewater, instead of becoming a disposal problem, becomes a resource that supports fish farming and agriculture, creating income for thousands of families while reducing pollution.
From sewage-fed fisheries to flood protection, the East Kolkata Wetlands turn waste into resources and demonstrate how cities can work with nature. Photograph: (The Guardian)
It is a rare example of how traditional ecological knowledge can complement modern climate resilience.
A model worth protecting
Despite its global recognition, the wetlands face mounting pressure from illegal encroachments, urban expansion, and pollution. Experts warn that shrinking these natural buffers could leave Kolkata more vulnerable to flooding while threatening biodiversity, food production and livelihoods.
The recent scenes from rain-hit cities remind us that floods are not caused by rainfall alone. They are often the result of disappearing lakes, wetlands, mangroves and floodplains that once gave water a place to go.
As urban flooding intensifies across India, Kolkata’s wetlands offer a powerful reminder that natural landscapes can be some of our strongest climate defences. Photograph: (Scroll.in)
As India prepares for more unpredictable monsoons, the East Kolkata Wetlands offer an important reminder: we do not always have to create bigger drains or taller walls. Sometimes, it is about protecting the ecosystems that have been doing the job all along.
In an era of climate uncertainty, this living landscape shows that working with nature may be one of the most effective solutions we already have.
