<p>The Yellow River, recognized as the cradle of Chinese civilization, has experienced significant environmental transformations due to rapid urbanization, which has substantially increased wastewater discharge into its basin, thereby altering its hydrological and water quality dynamics. Based on nearly a decade of monitoring data from over 20 sections within the Dahei River basin, a pivotal tributary at the upper reaches of the Yellow River, this study analyzed the variations in seven key water quality parameters (TN, TP, NH₃-N, COD, BOD₅, DO, and COD_Mn) across regions influenced by varying degrees of human activity and differing climatic conditions over wet, normal, and dry years. The results indicated that the most suitable model for fitting the ‘hydrological frequency-water quality’ relationship over time was linear. The R² values ranging from 0.82 to 0.99, suggesting strong reliability of the model. Generally, the water quality concentrations exhibited gradual changes over time. Spatially, the preferred model for the ‘hydrological frequency-water quality’ relationship was exponential, with a greater likelihood of sudden increases in water quality concentrations, supported by R² values ranging from 0.85 to 0.99, indicating dependable fitting. During various periods, the water quality in high-activity areas consistently exhibited poorer water quality compared to the low-activity areas. Indicators negatively impacting water quality were 1.66–63.25&#xa0;times higher in high-activity areas than in low-activity areas. Water quality was generally poorer during wet years. For example, total nitrogen (TN) concentrations exceeded the Class V water standard (2&#xa0;mg/L) in all river sections during wet years, with 81.05% of sections surpassing this threshold in normal years and 90.36% in dry years. These findings offer valuable insights for basin managers, highlighting the need for targeted interventions to mitigate water quality deterioration and enhance pollution control strategies.</p>