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Background & Aims of the Study: Water resources are useful or potentially useful. Uses of water are included agricultural, industrial, household, recreational and environmental activities. The majority of human uses require fresh water. Rivers are parts of this fresh water that play a very important role in the water cycle, acting as drainage channels for surface water. Hence, regular monitoring program and water quality control are the most important strategies to reduce pollution and improve the quality of water. The aim of this study is the evaluation of surface water quality by NSFWQI index and pollution risk assessment, using WRASTIC index in 2015.

Materials and Methods: In this study, the analytical survey, experimental studies and investigation of references in the context of library studies have been used. Water quality data collected from 7 sampling sites during 4 seasons from March to February 2015 and quality parameters including dissolved oxygen, pH, total dissolved solids, biochemical oxygen demand, turbidity, temperature, phosphate, nitrate and fecal coliform were examined by standard method. Data were analyzed by National Sanitation Foundation Water Quality Index. Then WRASTIC index (Wastewater-Recreational-Agricultural-Size-Transportations avenues- Industrial -cover of vegetation) is used for risk assessment in basin.

Results: NSFWQI index results showed that water quality in the river station 1 (Morkan) is located in the middle class and other stations in all seasons have bad quality. The worst situation (bad quality) was related to the bridge Chum and Varzaneh in autumn with an average of 29 and the best quality is relevant to Morkan station in summer with an average of 59. The finding of WRASTIC index represent that watershed is located in high risk class with the value of 70.

Conclusion: Based on the results of this study, the pollution from station 1 toward the subsequent stations have increased significantly and the river water quality has been reduced. In addition, agricultural, industrial activities and population centers are the main causes of Zayandehrud river pollution. Therefore, the management plans to protect of this valuable river is necessary.