Irrawaddy Dolphins of Chilika Lake: India's Rarest Cetacean in Brackish Waters

Roughly 150 Irrawaddy dolphins live in Chilika Lake, making this the largest known population of the species in any single enclosed water body on earth. They are not the acrobatic, open-ocean dolphins of wildlife documentaries. Orcaella brevirostris, the Irrawaddy dolphin's scientific name, has a blunt, rounded head with no visible beak, a flexible neck that allows it to turn its head sideways, and a small, low dorsal fin set far back on the body. They look, at first glance, more like a beluga than a bottlenose.
The biological distinction that sets them apart from most cetaceans is their capacity to move between marine, brackish, and freshwater environments. A 2008 IUCN assessment formally split the species into distinct subpopulations, marine, estuarine, and riverine, because the ecological pressures on each group differ enough to warrant separate conservation assessments. The Chilika population sits in the estuarine category. These dolphins produce clicks and buzzes for echolocation but are notably quieter than open-ocean species, an adaptation researchers at the Wildlife Institute of India have linked to the acoustic complexity of shallow, vegetation-dense lagoon environments.Chilika is India's largest coastal lagoon, stretching across roughly 1,100 square kilometres along the Odisha coast. It connects to the Bay of Bengal through a narrow channel, and three rivers, the Daya, Bhargavi, and Nuna, feed freshwater into it from the north. The result is a water body that is neither sea nor river. Salinity shifts with the season: low after the monsoon when river inflow peaks, higher in summer when evaporation and tidal exchange dominate. The dolphins move through this salinity gradient constantly.
The Satapada region, in the outer channel area where the lagoon meets the sea, is where sightings are most reliable. Boat operators there have built an informal dolphin-watching economy around the population. The dolphins surface in small groups, typically three to six individuals, and occasionally spit water, a behaviour observed in Irrawaddy dolphins across their range in Southeast Asia, from the Mekong to the Ayeyarwady, though its precise function is still debated among cetacean biologists.The Chilika Development Authority has tracked the dolphin population since the early 2000s. The numbers held relatively stable through the 2010s, but the pressures on the lagoon have not. Siltation from the three feeder rivers is reducing water depth in the northern sector, shrinking usable habitat. Illegal fishing with monofilament gill nets remains the most direct threat to individual dolphins: the animals become entangled and drown. Motorised boat traffic in the outer channel has increased with tourism, raising underwater noise levels that interfere with echolocation and, by extension, foraging.
Pesticide runoff from agricultural land surrounding the lagoon accumulates in fish, which the dolphins eat. Studies published by the Zoological Survey of India have detected organochlorine compounds in Chilika's fish populations, the same class of chemicals that contributed to dolphin population collapses in other South Asian water bodies during the 1980s and 1990s. The Irrawaddy dolphin is listed as endangered on the IUCN Red List, and the Chilika subpopulation has no buffer: there is no second lagoon to fall back on.The Chilika Development Authority, working alongside the Odisha Forest Department, has designated dolphin reserve zones where motorised vessels are restricted. Fishermen in the Satapada area have been brought into community monitoring programmes, reporting strandings and entanglements in exchange for compensation and gear that reduces bycatch risk. These are not large-scale interventions. They are patch-by-patch efforts to reduce the most direct causes of mortality while the larger problems, siltation, agricultural runoff, climate-driven salinity shifts, remain structurally unresolved.

The Irrawaddy dolphin has no flagship status in India comparable to the Gangetic river dolphin, which is the national aquatic animal. Chilika's dolphins exist in a policy gap: they are not freshwater dolphins, so they fall outside the Gangetic conservation framework, and they are not marine mammals in the open-ocean sense, so they receive less attention than sea-facing cetacean programmes. Their in-between nature, the same biological trait that allowed them to colonise Chilika in the first place, has made them administratively invisible in ways that matter for funding and legal protection.
The lagoon itself is what keeps this population alive and what is slowly changing around it. A dolphin that can live in brackish water survived because it was adaptable. Adaptability has a ceiling, and Chilika is approaching the conditions that test it.