<p>Yinghu Lake in Ankang City, Shaanxi Province, serves as a critical water source for the Danjiangkou Reservoir, the core water-receiving body of the Middle Route of the South-to-North Water Diversion Project. To safeguard its aquatic ecological environment, the comprehensive trophic level index method was adopted to assess the trophic status of Yinghu Lake, based on in-situ monitoring data collected during April-June 2019, April-August 2021, April-June 2022, March-August 2023, and March-September 2024. Concurrently, principal component analysis (PCA) was applied to identify the dominant components associated with eutrophic conditions. The results showed that: (1) In part of the time from March to September, the pH of Yinghu Lake repeatedly exceeded the standard, exceeding the Class V standard of surface water. Correlation analysis between pH value and main water quality factors indicated that the excessive pH was related to algal growth, which in turn was associated with the nutritional status of the water environment; (2) The average comprehensive nutrient status index of Yinghu Lake was 39.364, which belonged to the medium nutrient level. (3) Principal component analysis showed that turbidity, algal density and chlorophyll a were dominant components associated with eutrophic conditions, while total nitrogen, ammonia nitrogen and total phosphorus were underlying nutrient factors contributing to eutrophication potential. Studies have shown that nitrogen and phosphorus are potential factors contributing to eutrophication potential and pH abnormalities. Therefore, the water ecological environment of Yinghu Lake should be protected by long-term means to control the nutrients in the lake body, and the biological method is safer and the treatment cost is lower.</p>