The present work is an attempt to assess the hydrobiological parameters which included, physico-chemical parameters, zooplanktons, molluscans and the availability of fish fauna was undertaken in the Karanja reservoir located in the northern part of Karnataka. The study was carried out for a period of two years from October 2001 to September 2003. The interesting findings from the study may be summarized as below.The climate of Bidar district is semi arid characterized by precipitation during southwest monsoon season which extends from June to September, overlapping and extension beyond the specific period. Rainfall plays a significant part in regulating the seasonal biological rhythms of different parameters in the reservoir. The atmospheric and water temperature followed a seasonal trend and varied at different times of a day and different months of the year. The temperature fluctuation in water was influenced considerably by air temperature, humidity, winds and solar radiation.