Lake Sentarum National Park (LSNP) is a Ramsar site located in the Upper Kapuas Regency, Province of West Kalimantan, Indonesia. This national park is an unique freshwater fish habitat formed by flat basin or floodplain with fluctuated water level throughout the year in response to rainfall and supply of water from the Kapuas River system. This study aims at describing the fish diversity variation in the LSNP caught using gill nets during high water period (rainy season) in March, June, October 2013, and June 2014 and during low water period (dry season) in March 2014. Samples were taken in three locations, ie River Tawang (outlet), Lake Pengembung, and Lake Belida. Six orders, 15 families, and 39 fish species were found. The total number of species found during the low water depth period was less (20 species) than that during high water depth period (32 species).'Flood-pulse'cycle and the corresponding rise and drop of water level in the floodplain area, sustained by aquatic productivity and habitat diversity, are considered to be the responsible hydrologically controlled seasonal variation in the study area.