Abstract: Algal blooms (ABs) are one of the key tasks in water environment management in Dianchi Lake. In this study, based on the information ABs information was extracted using MODIS data from 2001 to 2023, spatiotemporal variations of algal blooms in Dianchi Lake were analyzed. Using correlation analysis, multiple linear regression, and path analysis, the effects of climatic factors and nutrient levels on the interannual variation of cyanobacterial blooms and their interactions were quantitatively analyzed. The results showed that (1) during the study period, the average annual frequency of algal blooms in Dianchi Lake was 56.8 %, and the annual cumulative area was 430.4 km2. The ABs outbreak period generally occurs from late May to late October every year. Spatially, the frequency of ABs was the highest in the northern Waihai region of Dianchi Lake, followed by the eastern and western coasts, and lowest in the central and southern regions of the lake. In the past 23 years, both the frequency and area of ABs have exhibited a decreasing trend, with bloom onset progressively delayed, termination occurring earlier, and duration shortened, reflecting a marked improvement in the status of ABs.(2) Overall, higher air temperature or lower wind speed promoted an earlier onset of ABs, whereas increased precipitation or reduced wind speed delayed bloom termination. The influence of meteorological factors on ABs varied seasonally: air temperature had a non-significant positive correlation with ABs frequency in winter (P > 0.05) but was significantly negatively correlated with ABs area in summer and autumn. (3) The critical temperature for the resurgence of bloom-forming algae in spring was 11–12 °C, and an earlier date when the daily mean air temperature was first persistently maintained above this threshold corresponded to an earlier onset of ABs. (4) Both meteorological and nutrient factors jointly influenced the occurrence of ABs, but the dominant factors differed markedly between the frequency and area of ABs occurrence. ABs frequency was mainly driven by the maximum air temperature in February, minimum air temperature in the rainy season, winter precipitation, and total phosphorus (TP) concentration, whereas the ABs area was primarily determined by the minimum air temperature in the rainy season and total nitrogen (TN) concentration. At present, meteorological factors are the dominant drivers of the interannual variation in the frequency of algal blooms in Dianchi Lake, whereas their influence on ABs area is relatively limited. These findings provide a scientific basis for the effective management and control of ABs in Dianchi Lake.