AbstractSurveys for shushuks Platanista gangetica were conducted during January to April 1999 in Kaptai Lake and the southern rivers of Bangladesh. A population of at least 125 dolphins was recorded in the Karnaphuli and Sangu rivers and connecting canal. The overall encounter rate was 0.76 dolphins per km. Density was highest in the lower reaches of the Sangu, where we recorded 1.36 dolphins per km. These rates are fairly high when compared with other areas of shushuk distribution. Dolphin movements in the Sikalbaha–Chandkhali Canal were consistent with it being used as a corridor for migration and dispersal between the Karnaphuli and Sangu. Shushuks were also sighted in marine waters of the Karnaphuli and Sangu river mouths, adding credibility to the hypothesis that dolphins move along the coast between the Ganges–Brahmaputra–Meghna and Karnaphuli–Sangu systems, perhaps during the monsoon when freshwater plumes extend into the Bay of Bengal. No dolphins were nobserved in Kaptai Lake, a dam-created reservoir of the upper Karnaphuli, despite reports of occasional sightings by local fishermen. No shushuks were observed in the Bagkhali and Matamuhuri rivers, possibly because of seasonal-closure dams present near the mouths of both rivers. The main threats to dolphin survival in the Karnaphuli-Sangu system are probably accidental entanglement in monofilament gillnets, bioaccumulation of persistent contaminants and possibly collisions with motorized vessels and a decline in prey as a result of over fishing. The most significant conservation measure that could be taken would be to establish a protected area for dolphins in the Sangu River below the Dohazari Bridge.