The Aras River has 1072 km long and is the longest Iranian internal river. The water of this river supplies drinking and industrial water to the cities of Poldasht, Aras, Parsabad, Marand, Jolfa, Hadishahr and other cities and villages of the route. Aras River is one of the most important rivers in Iran; in addition, of providing drinking water to some cities and villages in the West and East Azerbaijan, in this research, we tried to evaluate the quality of the Aras River using the IRWQISC index. For this purpose, along the Aras River in the 50 km range above the Aras dam, five sampling stations were selected and conducted for monthly intervals of microbiological and physico-chemical sampling. For each sample, then, using the IRWQI index, water quality at each station was evaluated on monthly intervals for six months.
The average of WQISC index for six months at stations 1 to 5 are 56.6, 52.5, 47.7, 39.4, and 34.9, respectively. Regarding the numerical value of the water quality index, index at station 1 is relatively good, stations 2 and 3 are moderate, and stations 4 and 5 are relatively bad.