As a key sensitive area of water quality safety in Danjiangkou Reservoir, the bay has become the focus of water quality security work in the reservoir area. Based on the long-term monitoring data from 2015 to 2024, this study systematically analyzed the spatial and temporal distribution characteristics of water quality indicators and comprehensive nutritional status index TLI (∑) in the bay, and discussed the correlation between the nutritional status of the bay and the algal proliferation intensity and the correlation between the two and the water environmental factors. The results show that in the past ten years, The concentration changes of the main water quality indexes in the bays of Danjiangkou Reservoir show different characteristics. The average concentrations of TN and TP monitored in the past were 1.08 ~ 2.34 mg/L and 0.019 ~ 0.132 mg/L, respectively. The average value of TLI (∑) is between 31.05 ~ 51.26, and the nutritional status of the reservoir bay is generally mesotrophic. The results of trend analysis show that the TP concentration and TLI (∑) of the reservoir bay show a significant downward trend. There is a mutation point in TLI (∑) between May and October 2018, which is related to the long-term implementation of water quality security work in the reservoir area and upstream and the regulation of high water level conditions on the water quality of the reservoir bay. In terms of seasonal variation, the concentrations of water quality indicators in the bay were generally at a low level in winter. In the autumn flood season of some years, there were many extreme rainfall events, and the reservoir water level rose sharply. The concentrations of TN and CODMn in the bay increased significantly, but the concentration of TP decreased significantly. In terms of spatial distribution, the water quality of the bays in the reservoir tail areas of both the Hanjiang and Danjiang Reservoir areas is relatively poor, and the risk of eutrophication in local reservoir bays is high. The results of correlation analysis and variance decomposition showed that the TLI (∑) in the bay was mainly closely related to the pollution input process, and the growth of algae in the bay was more significantly affected by the physical and chemical indexes of the water body, especially WT. The results of this study can provide scientific basis and decision-making reference for the prevention and control of eutrophication and algal blooms in the Danjiangkou Reservoir Bay.