Anzali Lagoon with 217 km^2 area is located on the south of Anzali port. Those which enter to lagoon are running through a watershed area of 347000 hectare. In the year 1990 monthly sampling were conducted on eleven rivers ended to Anzali Lagoon. In order to found out standard water quality index for those rivers, the physicochemical parameters such as temperature, orthophosphate, ammonia, nitrate, chemical oxygen demand and total suspended solid has been determined. With the aid of rating curve the quality index for each sampling station were determined, and the eleven rivers has been classified accordingly. The result indicate that the Pirbazar River with respect to pollution is more critical, because first the most industrial activities are concentrated in the watershed area of this river and second this river is receiving the untreated domestic wastewater of the Rasht which is the biggest city of Guilan Province. This huge amount of pollution interfere with the self-purification action of the river, the other ten rivers are relatively in better condition compare to Pirbazar
