Endangered dolphins survive in a Bangladesh river so polluted it’s ‘not livable’ for fish

At least 20 endangered Ganges river dolphins still survive in Bangladesh’s extremely polluted Buriganga River, a 12-month study found, reports contributor Md Jahidul Islam for Mongabay. Skirting the southern edge of the country’s capital, Dhaka, the 29-kilometer (18-mile) river is recognized as one of the most contaminated urban waterways globally. Researchers surveyed a 27-km (16.7-mi) stretch of the river between September 2023 and August 2024, observing Ganges river dolphins (Platanista gangetica) in 10 out of the 12 survey months. Group sizes averaged about four individuals, with calves accounting for nearly 16% of sightings, signaling active reproduction despite severe ecological degradation. “The Buriganga is not a usual place for dolphins, where native fishes have largely vanished,” study co-author and researcher Md. Aminur Rahman told Mongabay. “When we found [the dolphins], we were amazed at how it was possible. Because the river is not livable for fish.” A 2025 study on the Buriganga River’s water pollution showed that it absorbs untreated industrial effluent from tanneries, textile dyeing plants, battery factories, and municipal sewage. Levels of toxic heavy metals, including lead, chromium, and cadmium, routinely exceed World Health Organization safety limits, driving dissolved oxygen levels near zero during the dry season, the study reads. While native fish species have collapsed, pollution-tolerant invasive suckermouth catfish (Hypostomus plecostomus), native to South America, have multiplied rapidly, Rahman said. Mohammad Abdul Aziz, study co-author and zoology professor at Jahangirnagar University in Dhaka, told Mongabay that the dolphins have likely adapted their diet to survive on these invasive fish. “Right now, the Buriganga is full of suckermouth catfish. We believe the dolphins are hunting these fish,” he said. Nationwide, a joint survey by Bangladesh’s Forest Department and WCS Bangladesh recorded 2,307 Ganges river dolphins across 4,900 km (3,045 mi) of the country’s rivers. “If we want to conserve the dolphins in the Buriganga, the priority must be to stop the pollution,” Aziz said, adding that saving the species requires eliminating destructive fishing practices and curbing industrial discharges. Read the full story by Md Jahidul Islam here. Banner image: A recent survey found that around 20 Ganges river dolphins survive in the polluted Buriganga River. Image courtesy of Md. Aminur Rahman. Credits Topics