Zooplankton community grazing rates as percentage of algae cleared per dayrn(%G/d) were determined in Lake Arsedi by in-situ feeding experiments (withrnchanges in chlorophyll a concentration method) using 1 l incubation clear glassrnbottles at two sampling sites (Littoral and open water). In replicated treatments,rnzooplankton and phytoplankton size fractionation experiments were done and thernresults indicate that invariably the larger zooplankton had higher % G/d than thernsmaller-sized ones, and the smaller-sized phytoplankton were easily removed byrnzooplankton than the larger-sized ones. Observations and experiments revealedrnthat zooplankton community composition; abundance and food density werernimportant factors determining grazing rates in this lake. Monthly variation in %rnG/d was caused by changes in zooplankton and phytoplankton communityrnstructures. During October 2005-February 2006 massive blooms of therncyanobacteria, especially Microcystis aeruginosa reduced grazing impact,rnwhereas during March-April 2006, diatoms and small flagellates dominated thernphytoplankton and were highly vulnerable to grazing by both cylopoid andrncalanoid copepods, although calanoid copepods had much stronger effect.rnIncreased copepod grazing during this period resulted in low phytoplanktonrnbiomass (the clear â€“water period). These results suggest that variation in thernstrength of grazing in eutrophic lakes such as Hora (Arsedi) result from changesrnin zooplankton and phytoplankton densities and community structure. Thernfindings of this study are believed to lay a basis for further research andrnconsequently to solve the problem of eutrophication by reducing external nutrientrnloading and controlling internal ecological processes.