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The Jialing River, a key watershed in the upper Yangtze River, faces challenges in maintaining stable water quality due to its extensive area and issues such as agricultural and cross-border pollution. This study examines the water quality variations in the Jialing River's main course and its two major tributaries, Fujiang and Qujiang, using 2021 monitoring data for five water quality indicators: dissolved oxygen, permanganate index, ammonia nitrogen, total phosphorus, and total nitrogen, across 48 river sections. Methods including Fuzzy Comprehensive Evaluation, Nemerow Index, and Nearest Neighbor Analysis were applied. The findings reveal that: 1 The Fuzzy Evaluation method effectively demonstrates the impact of each indicator on various water quality standards. 2 In the study area, 38 sections are rated below Grade III for total nitrogen, and one section is rated Grade IV for permanganate index, indicating significant pollution of total nitrogen and exceedances of permanganate standards. Agricultural activities are identified as a major contributor to the exceedances of these two indicators. The remaining three indicators meet the water quality control standards for the Jialing River. 3 Spatially, the sections with Class III water quality are the least in the main stream, indicating relatively optimal water quality, while the Fujiang exhibits the poorest water quality. Class V sections are mainly distributed in the middle and lower reaches, with better water quality in the upper reaches of the watershed. 4 Seasonally, the water quality of river sections categorized as Class III deteriorated during the dry season, with an increase of three sections compared to the wet season. The water quality during the dry season exhibited greater instability. Specifically, the Fujiang demonstrated relatively stable water quality throughout the year, whereas Qujiang exhibits a decreasing trend in the number of Class V sections from July to December, indicating an improvement in water quality during the year. Conversely, the main stream shows an increase in the number of Class V sections from July to December, suggesting a declining trend in water quality during this period. These results offer valuable insights for pollution control and aquatic ecosystem restoration in the Jialing River basin. [ABSTRACT FROM AUTHOR]