The zooplankton of a crater lake in Ethiopia, Babogaya, was sampled at 3rnstations from June 2006 to April 2007 concurrently with phytoplanktonrnnumerical abundance. The spatial and temporal variation in abundance of therndominant crustaceans, Rotifera, Copepoda and Cladocera is discussed.rnTemporal (months, sampling dates) variation was larger than spatial (station)rnvariation for the mean total zooplankton. All major zooplankton groups showedrntemporal variations in abundance, with highest densities during wet (June tornAugust) and mixing period (November to January), minimum densities after thernend of the big rain in October. Rotifers were the dominant group and made uprnalmost 71% of the total zooplankton abundance. Rotifers showed a maximumrndensity during the dry period and declined after the end of the big rains.rnCopepods and cladocerans also contributed 23% and 6%, respectively, of thernmajor total zooplankton abundance of the lake. The maximum verticalrndistribution of total zooplankton was observed at the metalimnon region. Thernphytoplankton community was dominated by dinoflagllates during the dryrnseason and there was a shift in dominance to diatoms during the long rainyrnperiod. The dominant phytoplankton showed distinct seasonality. This study isrnbelieved to give a baseline for further research on zooplankton seasonalrnvariation and production that helps in the understanding of fish production andrnproper management in the study lake.rnKey words: Lake Babogaya, zooplankton, phytoplankton, temporal dynamics,rnvertical migration.