The fish diversity of the Garga reservoir was studied. Garga reservoir of Bokaro has been constructed on river Garga. The water of the reservoir is used for irrigation, fishery and drinking purposes. Fish collections were done with gillnets of standardized dimensions with several mesh sizes. 25 fishes were identified during the study belonging to Cyprinidae 11 species, Channidae and Notopteridae of 2 species, Bagridae with 4 species and a species each of Mastacembelidae, Cichlidae, Anabantidae, Siluridae, Saccobranchidae and Claridae. The species diversity is peak in post monsoon, coinciding with favourable conditions such as sufficient water and ample food resources whereas the diversity was low in pre-monsoon probably due to the shrinkage of the water spread of the reservoir.