On 1st June 2003, the Three Gorges Reservoir (TGR) began its storage officially, and the water level reached at 135 fit on 10 June (and at 139 in on 5 November). Three are a lot Of tributaries been flooded in the lower reaches, and many bays are therefore formed front that time in the reservoir. We monitored the changes of ecological environment of TGR, and found that most of bays was in eutrophic state and emerged several Serious algal blooms predominated by dinoflagellate (Peridiniopsis spp.) and diatom (Cyclotella sp.), especially in spring. In case of Xiangxi Bay, the largest one in Hubei part of TGR and the one most. close to the dam, the monthly monitoring of 2 years shown that the trophic state in most. month was eutrophic, except in winter. Farthermore, the trophic state in spring was hyper-eutrophic. On the other hand, to get a general information of eutrophicalion situation in TGR, we assessed the trophic state of 2 bays and TGR itself in spring, 2005. The results shown that 5 bays (22.7%) were in meso-trophic, and 17 bays (77.3%) were in eutrophic (10 bays in hyper-trophic, occupied 45.5% The water quality of TGR itself, however, was still in good condition (meso-trophic), due to its fast exchange rate of water. Statistic analyses shown that relationship between chlorophyll a and watershed characters (annual discharge and catchment. area) of bays in TGR was significant negative. It implied that, generally, the smaller of the bay (or its annual discharge), the higher of chlorophyll a concentration, i.e. the easier of forming algal bloom in spring. Based on the monitoring and researching, we discussed and proposed several strategies to control or mitigate eutrophication phenomena in TGR, including pollution control, complete survey, mechanism study and eco-hydraulic regulation.