This study utilized a combination of satellite remote sensing imagery and machine learning classification methods to monitor a rare large-scale algal bloom event in Lake Qionghai(Sichuan) from February to March, 2022. Preliminary investigation into the possible causes of this widespread algal bloom event was conducted from the perspectives of temperature, wind speed, nutrient levels, and aquatic vegetation distribution. Remote sensing monitoring revealed that on February 18, 2022, algal blooms began to appear, with the bloom area gradually increasing in the lake. By March 10, the bloom reached a maximum area of 13.67 km² (accounting for 50.63% of the total water surface area), after which the bloom area gradually decreased, and disappeared since March 19. Based on simulated data, it was found that Lake Qionghai experienced a warming rate of 0.14 ℃ per decade between 1985 and 2022. Furthermore, there was a significant negative correlation between water temperature and the area of aquatic vegetation. In comparison to the 2000s, the nitrogen and phosphorus nutrient concentrations in Lake Qionghai did not show a significant increase and exhibited reduced fluctuations from 2010 to 2020. However, extensive degradation of aquatic vegetation was observed with aquatic vegetation coverage decreasing by 0.19 km² every decade, 0.10 km² among which are submerged vegetation. Our analysis suggested that from a macro perspective, under the multiple stressors of climate change and rising water levels, the degradation of aquatic vegetation exacerbated, favoring the dominance of phytoplankton in Lake Qionghai ecosystem. The rapid increase in temperature, low wind speeds, and lack of rainfall from February to March, 2022 also facilitated the algal bloom formation. The sustained increase in water temperature promoted stratification of the water column, which also provided favorable conditions for the growth of phytoplankton. However, the causes of the occasional widespread algal bloom formation in Lake Qionghai require further investigation. Under future climate change scenarios, algal bloom risks will still exist in a relatively clean water like Lake Qionghai and this warrants continued attention.