Rivers can be contaminated with different pollutants such as trout farms. Evaluation of the effect of trout farm on water quality is important to give new permission for trout farm construction. In current work, the effect of constructed trout farms near the Deinachal River on some physicochemical properties namely chemical oxygen demand (COD), biological oxygen demand (BOD5), dissolved oxygen (DO), pH, temperature, turbidity, nitrate, nitrite, phosphate, heavy metals, total hardness, total alkalinity, calcium, magnesium, electrical conductivity, fecal coliform and ammonium were studied and the water quality was classified using Iran Water Quality Index (IRQWI). Results showed that except nitrite, ammonium, chromium, nickel, lead, cadmium and mercury, other parameters affected by both trout farms and domestic wastewater. However, assimilative capacity of Deinachal River due to entrance the branches into the river can improve the water quality.