Chlorophyll-a is an important indicator of primary productivity in lake ecosystems, and its concentration changes reflect the nutrient status and ecological health of the water. This study, based on water quality and environmental data from 2011 to 2024 for Chagannaoer, uses correlation and redundancy analysis to reveal the interannual and intra-annual variation characteristics of chlorophyll-a concentration and its key driving factors. The results show that between 2011 and 2024, the interannual variation of chlorophyll-a concentration in Chagannaoer was stable, with the highest concentrations in summer and the lowest in spring, and a decreasing trend from north to south. Interannually, chlorophyll-a concentration was negatively correlated with the permanganate index and positively correlated with water volume, water depth, precipitation, evaporation, and temperature. Runoff also had a promoting effect on its concentration.