Beel is one of the ancient types and obviously a fascinating one due to its biodiversity and ecological importance in local and national perspective of Bangladesh. The Bhawal beel is one of important beels and excellent habitat for small indigenous species (SIS). The present status and decline causes of Bhawal beel was studied from March 2016 to February 2017. Data collection was carried out from four villages of Achim union under Fulbaria upazila. Questionnaire Interview (QI), Focus Group Discussion (FGD) and cross-check Interview were done to obtain data related to status and decline causes of fishes from the fishermen and resource person. A total of 56 species of fish including prawn under 10 orders and 23 families were recorded from thebeel. Cypriniformes (33.93%) was the most dominant order followed by Siluriformes (21.43%), Perciformes (19.65%), Channiformes (7.14%), Synbranchiformes (7.14%), Decapoda (3.58%), Cyprinodontiformes (1.78%), Osteoglossiformes (1.78%), Beloniformes (1.78%) and Tetraodontiformes (1.78%). Among the recorded families Cyprinidae was the most dominant family contributing 17 species. The availability status of observed species were remarked in four categories and obtained as available (44.64%), seasonal (19.64%), rare (16.08%) and very rare (19.64%). Decline causes like overfishing, use of illegal fishing gear, siltation, katha fishing, and abstraction of water for irrigation, catching of fry and brood fishes, lack of connection of beel with Banar river and absence of proper beel management policy were observed as major threats for fish diversity. About 13species were found threatened (1 critically endangered, 5 endangered and 7 vulnerable) which may extinct in near future due to proper management of the beel fishery. The present study recommends minimizing of all these impediments. Besides Community Based Fisheries Management (CBFM) and beel nurseryis essential to save the valuable fish diversity of Bhawal Beel on which local livelihood depends.