This research evaluated fish species diversity and hydrological parameters in northwest Bangladesh’s Roktodaho beel between Bogura and Naogaon from July 2020 to June 2021. Firsthand assessment surveys, focus group discussions, and questionnaire-based in-person interviews gathered four monitoring stations’ monthly data. 33 fish species from six taxonomic orders and 17 families were detected in the beel. 66.67% were least concerned, 15.15% were vulnerable, 6.06% were endangered, and 3.03% were extremely endangered. The reported fish orders were Cypriniformes (30.31%), Siluriformes (24.24%), Anabantiformes (21.21%), Synbranchiformes (12.12%), Ovalentaria (9.09%), and Gobiiformes (3.03%). The IUCN Bangladesh 2015 report found 11 fish species, including 1 extremely endangered, 2 endangered, and 3 vulnerable. Ompok pabda, Botia dario, and Mastacembelus armatus lived in the study area. Temperature, water depth, pH, dissolved oxygen, and total alkalinity were assessed. All hydrological indicators were within fish-cultivation ranges. Nine phytoplankton genera and three zooplankton genera were discovered, with Chlorophyceae and Crustacea dominating, respectively. Waterweeds numbered nine. Risks in the study area included uncontrolled overfishing, environmental deterioration, dewatering streams, katha fishing, outdated fishing equipment, and more. Reducing human impacts, adopting fishing rules, creating and maintaining fish sanctuaries, and raising awareness may conserve fisheries assets.