In 2022, frequent cyanobacterial blooms occurred in Lake Hulun, covering nearly the entire lake surface, degrading aquatic landscapes, and posing serious threats to ecosystem health. To investigate the drivers of these large-scale blooms, water samples were collected from surface, middle, and bottom layers at 13 sampling sites during spring, summer, and autumn of 2022. Cyanobacterial species composition, abundance, biomass, and key water quality indicators were analyzed. A total of 22 cyanobacterial species were identified, with 10 dominant groups observed over the study period.Microcystis spp. remained the dominant genus across all seasons. The abundance and biomass of cyanobacteria varied significantly in different periods and depths. The abundance (2.58×10⁹ cells/L) and biomass (3.30×10² mg/L) of cyanobacteria in summer were 1-2 orders of magnitude higher than those in spring and autumn. In spring, the abundance and biomass of cyanobacteria were the highest in the bottom layer of the lake, and the highest in the surface layer of the lake in summer and autumn. Correlation and redundancy analyses revealed seasonal differences in influencing factors, identifying water temperature, nitrogen and phosphorus concentrations, dissolved oxygen, and pH as key environmental drivers of bloom dynamics. For management, we recommend moderate nutrient control with a dual nitrogen-phosphorus reduction strategy, along with enhanced bloom prediction, early warning, and emergency response capabilities. These measures are essential for mitigating bloom risks in eutrophic lakes such as Lake Hulun and may inform future cyanobacterial bloom control strategies in similar ecosystems.