The intensification of global warming has led to a significant increase in the frequency and intensity of heatwave events. Exploring their impact on ecological processes such as lake nutrient salts, chlorophyll-a (Chla), and phytoplankton growth is crucial for understanding the ecological response and feedback mechanisms of lakes under heatwave conditions and providing scientific support for lake management and regulation under climate change. This study, based on the GOTM-WET model, simulated the impact of the 2022 summer heatwave on Chla concentration in North Taihu Lake, with a focus on analyzing the effects of different heatwave intensities on Chla and their possible mechanisms. The results indicated that the 2022 summer heatwave significantly suppressed Chla concentration, and the inhibitory effect intensified with the increase in heatwave intensity. Further analysis revealed that the maximum water temperature during the 2022 heatwave exceeded 37°C, possibly surpassing the optimal growth temperature for most algae, thereby inhibiting their growth. Additionally, the heatwave intensified water column stratification, leading to a reduction in total nitrogen (TN) and total phosphorus (TP) concentrations in the surface layer and their accumulation in the bottom layer. This vertical differentiation of nutrients limited the nutrient supply required for surface algae growth, further suppressing the increase in Chla concentration. This study revealed the potential impact mechanisms of dual factors of water temperature and nutrients on lake algae growth under extreme high-temperature conditions, deepening the understanding of the effects of heatwave events on lake ecosystem processes.