Nutrient reduction is crucial for controlling harmful algal blooms in Lake Chaohu, China. A new index called NLCI was used to assess the impact of nutrient loading on algal blooms. The study found that reducing phosphorus loading is key to controlling algal blooms in the lake. Both internal and external sources of phosphorus contribute significantly to the blooms, with Nanfei and Hangbu Rivers identified as hot spots for external phosphorus reduction. The best times for reducing external phosphorus are August, May, and July. This new index could help develop better strategies for nutrient reduction in other eutrophic lakes.