 The study analyses long-term and seasonal trends in the streamflow and water quality of the Guanting Reservoir Basin using a seasonal trend decomposition method, revealing that human activities have caused a decrease in streamflow and an improvement in water quality. The results suggest that for rivers with a sharp decline in streamflow, water pollution control measures can significantly improve water quality. This article was authored by Peng Cheng, Xu Yongli, Jing Jiangsu, and others.