The aim of this study was to assess the influence of trout farm effluents on water quality parameters in the Dohezar Stream. In this study two trout farms and 7 stations were selected and physiochemical of water, including air and water temperatures, dissolved oxygen concentration (DO), pH, electrical conductivity (EC), water flow and biochemical oxygen demand (BOD) were measured every 30 days for one year. A combined total of 60 benthic macroinvertebrate taxa were collected from the seven sites of the stream. The results showed that trout farms had a significant impact on EC, pH, water flow and BOD in the water throughout the year and among stations (p<0.05). Only DO did not show significant differences in the one year survey. Macroinvertebrates had significant differences in abundance downstream from the trout farm effluent, particularly in stations 1 and 3 compared with others. However, the diversity of benthic macroinvertebrates significantly decreased, particularly in stations of 3, 4, 6 and 7. Regarding benthic macroinvertebrates, the abundance percentage of ephemeropterans, plecopterans and trichopterans (expressed as EPT %), and Biological Monitoring Working Party (BMWP) were much lower in station 3 than in other stations
