Reservoirs, as a type of artificial lake, have their number and controlled water volume in China approaching that of natural lakes, making them an important component of China"s surface-based manageable static water resources. The hydrological processes, topography, and management/utilization patterns of reservoirs differ from those of natural lakes. Ecologically, reservoirs exhibit characteristics of both riverine and lake ecosystems, and their limnological mechanisms are unique. Establishing scientific observation field stations to conduct long-term ecological monitoring, in-situ experimental research, and the development of restoration technologies for reservoirs is of great significance for scientifically supporting the ecological and environmental security of reservoirs and the sustainable use of their resources. Taking the Qiandaohu Ecosystem Research Station of the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (referred to as the "Qiandaohu Ecological Station") as an example, this paper analyzes the achievements, hotspots, and challenges in the ecological research of large deep-water reservoirs based on 20 years of scientific observation, experimental research, and technology demonstration on the water environment and aquatic ecosystem of Qiandaohu Reservoir. Monitoring of water quality and ecological indicators at the Qiandaohu Ecosystem Research Station over the past five years indicates that the overall water quality of Qiandaohu Reservoir remains stable at an oligotrophic to mesotrophic state. However, key water quality monitoring sections still face risks such as unstable water quality and abnormal algal proliferation in local areas. Stratification of ecological and environmental indicators, such as thermal stratification, is evident, with significant seasonal variations and interannual fluctuations. Research shows that meteorological and hydrological events, such as warming, heavy precipitation events, and high-temperature droughts, have substantial impacts on the water quality and ecology of Qiandaohu Reservoir. Human activities, including changes in watershed land use and reservoir fishery management models, also profoundly affect the water quality and aquatic ecology of Qiandaohu Reservoir. Furthermore, technologies developed at the Qiandaohu Ecosystem Research Station, such as reservoir monitoring, water quality and algal bloom early warning, and ecological restoration of the reservoir, offer significant demonstration value for the ecological and environmental protection of similar source water reservoirs in China. Current research priorities for the Qiandaohu Reservoir aquatic ecosystem include integrated technologies for ensuring water quality safety in source water reservoirs, mechanisms of physical environmental changes (e.g., light, heat, and hydrodynamic processes) in reservoirs and their ecological effects, food web structures and ecological regulation technologies in large reservoirs, carbon cycling and greenhouse gas emission mechanisms in deep-water reservoirs, and digital twin and AI-based intelligent management technologies for reservoir water environments.