Abstract <p>Lake Chaohu, Hefei’s daily drinking water supply, has attracted much attention in recent years due to eutrophication and water quality deterioration. Based on daily water quality data from 2021 to 2023 at 20 National Assessment Cross-sections in Lake Chaohu Basin (LCB), this study analyzed the spatial and temporal variation characteristics of water quality and their influencing factors by using the water quality index (WQI) method through statistical analysis, associating with principal component analysis and correlation analysis. Furthermore, the water quality physicochemical parameters mainly include pH, dissolved oxygen (DO), chemical oxygen demand (COD_Mn), ammonia (NH₃-N), total nitrogen (TN), and total phosphorus (TP). The results revealed that: (1) Generally, the water quality state was classified as “moderate” in LCB (mean value of 69.1) (2) In terms of temporal variation, due to the high population density along the banks of the lakes and the numerous direct discharges of various types of wastewater, the water quality in LCB was found to be better than that of the surrounding basins; notably, the northern part of LCB exhibited the worst water quality (3) From a temporal variation perspective, influenced by meteorological factors such as temperature and precipitation, the water quality exhibited a trend of initially declining and then increasing across the four seasons, with winter and spring showing better water quality than summer and autumn. This research can provide a scientific basis for assessing the effectiveness of pollution control which can contribute to the sustainable management of water resources.</p>