Kolleru Lake
Asia's Largest Freshwater Lake · Ramsar Wetland · Kaikalur, Andhra Pradesh
Kolleru Lake doesn't look like what most people imagine when they hear 'Asia's largest freshwater lake.' There are no dramatic cliffs, no deep blue depths, no visible horizon of open water. What you find instead is something more interesting: a flat, shallow wetland that seems to blend imperceptibly into the surrounding rice fields. The water is rarely more than two metres deep. But it stretches across 245 square kilometres at its core — and in monsoon season, it expands far beyond that.
The lake exists because of deep geography. Kaikalur sits in the inter-deltaic basin between two of India's major rivers — the Krishna to the south and the Godavari to the north. Over thousands of years, sediment deposits from both rivers created a natural depression in the land. Rainfall accumulated. The Budameru and Tammileru channels carried overflow into this basin. Kolleru formed — not as a dramatic event, but as a slow geological inevitability. It is, at its core, a product of the two rivers that define this entire region.
Its most important function is one that rarely makes headlines: flood control. When the Krishna and Godavari carry exceptional monsoon flows, Kolleru absorbs the overflow before it can reach the coastal towns downstream. Without the lake acting as a natural buffer, the areas around Eluru, Bhimavaram, and the Krishna coast would face far more severe flooding. The lake is, in effect, invisible infrastructure — infrastructure that has been here for thousands of years and that the region depends on every single monsoon season.
Sunset at Kolleru — Grey Herons, Painted Storks & Black-headed Ibises · Wikimedia Commons CC BY-SA 4.0
As the heat rises, Kolleru contracts to its lowest water levels. The receding lake reveals dark, fertile silt on the exposed lake floor. Farmers have worked this temporary land for generations, planting and harvesting before the monsoon returns to reclaim it. In some years the shrinkage is dramatic — land that was underwater in January becomes a working field by May.
The lake transforms completely. As the Krishna and Godavari flood and the regional rainfall peaks, Kolleru expands well beyond its core 245 km² — swallowing roads, submerging low-lying settlements, and performing its critical function as a flood buffer for the coastal region. Villages close to the water's edge adapt — boats replace roads, houses sit on raised ground, and movement follows the water's logic.
This is Kolleru at its best. The water stabilises, the flooding recedes, and the lake settles into a calm that makes it both productive and beautiful. Migratory birds arrive from across Asia — from Siberia, Central Asia, and the Himalayan foothills — to spend the season here. The light is extraordinary at dawn and dusk: low sun, flat water, thousands of birds. October to March is the only time to come if you want to understand why this place matters.
Operation Kolleru
From the 1980s onwards, fish and prawn farmers began converting sections of the lake into aquaculture ponds — first hundreds, then thousands of them. By the 1990s, the encroachment had become severe. The lake was shrinking. The natural vegetation that birds needed for nesting was disappearing. What had been a wetland of 900 square kilometres was contracting toward its current core. The change happened fast enough that satellite images from the period show the transformation clearly.
The conflict was real and complex. Aquaculture had lifted incomes for thousands of families in the surrounding villages. Kaikalur's prawn and fish farming economy grew significantly during this period. But the lake that those livelihoods ultimately depended on was being destroyed in the process. When Ramsar status was conferred in 2002, the pressure for government action increased. Operation Kolleru — a court-ordered removal of illegal encroachments — followed, though its execution was contested and incomplete.
The lake today is partially restored but still under pressure. The Ramsar designation remains. Bird populations, though lower than their historical peak, return each winter. The story of Kolleru is cited in environmental law journals, policy papers, and conservation research across India as a landmark case study in wetland encroachment and the difficulty of reversing it.
Kolleru Lake is only 1–2 metres deep on average — yet it is Asia's largest freshwater lake by surface area.
Over 60 channels and streams feed water into Kolleru from the surrounding delta.
The lake is part of the Central Asian Flyway — one of the world's major bird migration corridors.
During monsoon, the lake can expand dramatically beyond its core boundaries, flooding surrounding low-lying land.
Kolleru was designated a Ramsar Wetland of International Importance on 19 August 2002.
Without Kolleru, Krishna and Godavari flood waters would reach coastal Andhra towns directly, with no natural buffer.