Abstract: The aim of this study is to assess the effect of aquaculture waste water on water quality of the receiving ecosystem. Vana rainbow trout farm was selected as a site of the study. There were four sampling stations around the fish farm along the Haraze river (200 m before and 200 m after farm, inlet and outlet of the farm) for water quality measurements. Waste excreted by fish did not increase nitrate and nitrite concentration at the releasing point but surprisingly a reduced phosphorous content was observed for the outlet water in comparison to station 1. Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD) were consistently higher for station 3 where waste water was released. However, the organic matter discharged was reduced in fall compared to winter. In conclusion fish farm effluent contains pollutant that can affect river water quality. However the pollutants magnitudes are too low to put a significant impact on the river ecosystem.