Lake Semayang and Melintang, East Kalimantan, as the habitat of freshwater dolphin

Semayang and Melintang are floodplain lakes, the lake water level are influenced by the Mahakam River. Annual water level fluctuation is up to four meters, implicates a flooding regime and modified the water quality, aquatic plant, and fish composition. Freshwater Dolphin (Orcaella brevirostris, Gray 1866) or in local name is Pesut inhabited the Mahakam River, between Muara Kaman to Long lram, spread out as far as 250 km. Lake Semayang andMelintang are one of the Dolphin habitat in Mahakam River system. The availability of fish in Semayang and Melintang lakes, especially whitefish group (Cyprinidae), fulfill the need of Dolphin food. Over fishing in Semayang and Melintang lakes is a threat to Dolphin existence, besides highsedimentation rate which shallow the lake, and due to mechanized water traffic.