Monitoring river water quality is a fundamental component of sustainable water resources management and aquatic ecosystem protection. This study aimed to review and analyze the water quality of the protected rivers of Mazandaran Province, including the Haraz, Chalous, Sardabroud, Nekarud, Tajan, Babolroud, and Dohezar-Tonekabon rivers, using the National Sanitation Foundation Water Quality Index (NSFWQI) and the Iran Water Quality Index for Surface Water Resources (IRWQIsc), and to identify the major factors influencing water quality variations. Relevant studies published in national and international scientific databases were systematically collected and comparatively analyzed. In addition, the relationships among electrical conductivity (EC), chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), dissolved oxygen (DO), ammonium, nitrate, phosphate, fecal coliform, turbidity, pH, and total suspended solids (TSS) were evaluated using Pearson correlation analysis and principal component analysis (PCA). The results showed that both water quality indices were strongly correlated with ammonium, COD, BOD₅, fecal coliform, and pH, whereas weak correlations were observed with TSS. PCA indicated that most of the variation in water quality was explained by two principal factors: organic pollution resulting from wastewater discharge and nutrient pollution associated with agricultural runoff. Comparative analysis further revealed a consistent decline in water quality from upstream to downstream reaches, with this trend becoming more pronounced in recent years. Among the studied rivers, the Sardabroud River exhibited the highest water quality, whereas the Haraz and Chalous rivers showed the poorest conditions. Overall, urban expansion, agricultural activities, municipal and industrial wastewater discharges, sand and gravel mining, and reduced river discharge during the dry season were identified as the primary drivers of water quality degradation. These findings provide valuable information for integrated river water quality monitoring and management in Mazandaran Province and other river basins in Iran.