An Isolated Population
In Asia's largest brackish water lagoon, Chilika Lake, lives a unique and isolated population of the Irrawaddy dolphin, Orcaella brevirostris. The latest census data from early 2026 indicates a stable population of 159 individuals in the lake. Chilika is the largest habitat for these dolphins in the world. Physically, the Irrawaddy dolphin is distinct; it has a blunt, rounded head and lacks the prominent beak common to many other dolphin species. Its flexible neck allows it to move its head in all directions.
The lake itself is a dynamic environment, a mix of fresh water from inland rivers and saline water from the Bay of Bengal. This creates a brackish ecosystem where salinity levels fluctuate with the seasons, decreasing during the monsoon and increasing during the dry summer. The dolphins here have adapted to this constantly changing aquatic environment. The population is considered physically isolated, with the nearest documented group of Irrawaddy dolphins located 250-300 kilometers to the north.
Genetic Divergence and Conservation
Scientific studies confirm that the Chilika Lake dolphins are genetically distinct from other Irrawaddy dolphin populations. Research on their mitochondrial DNA shows significant genetic differentiation when compared to populations in rivers like the Mekong or in the coastal waters of Thailand. This genetic divergence points to a long period of isolation, during which the Chilika dolphins evolved specific traits to survive in their unique lagoonal habitat.
This population faces threats, primarily from entanglement in fishing gillnets and disturbances from mechanized boat traffic related to both fishing and tourism. A major conservation success story has unfolded here. In the 1990s, the lake was suffering from siltation that choked its connection to the sea, reducing salinity and degrading the habitat. In 2000, the Chilika Development Authority (CDA) dredged a new mouth to the sea. This intervention restored the lake's salinity, flushed out sediment, and led to a seven-fold increase in fish landings. The improved habitat directly benefited the dolphins, whose population increased from around 70 before the restoration to over 150 in the years following. The lake was removed from the Montreux Record of threatened wetlands in 2002, a first for any site in Asia.