Assessment of river water quality is a crucial step towards sustainable watershed management. However, widely used international indices such as NSFWQI, OWQI, and CWQI are often unable to accurately reflect the local and ecological conditions of different regions. To address this limitation, the Iranian Surface Water Quality Index (IRWQISC) was introduced, but its application in different watersheds of the country still remains limited. The present study aimed to assess the water quality of Bagherabad River based on the local IRWQISC index to provide a more accurate and appropriate classification to local conditions. Sampling was conducted at five stations over an eight-month period (October 2022 to June 2023) and in three seasons: autumn, winter, and spring. Eleven physical, chemical and microbial parameters including pH, DO, BOD, COD, nitrate, phosphate, ammonium, electrical conductivity, turbidity, hardness and fecal coliform were measured according to standard protocols. Data were analyzed using LS Means test to examine spatial and seasonal variations and then IRWQISC index values were calculated. Results showed that IRWQISC index values fluctuated between 23.59 and 65.75 and water quality varied from relatively good to good. High COD and phosphate values indicate the impact of agricultural, domestic and industrial wastewater. Seasonal assessment also showed that water quality was better in winter than autumn and was at an intermediate level in spring. Comparative assessment showed that river water is suitable for agricultural and industrial uses but requires treatment for drinking.