The multidate and multistage satellite images and airphotos are used in the study of the deterioration of water environment in East Taihu Lake. By combining multidate images of RS with the data of water level on-the-spot, the three-dimensional analysis of lake basin is suggested, and the interpretations of developments in flow behavior, water quality, aquatic plants,and in the engineering of reclamations, dikes, canals, and floodgates have been made. It is believed that the deterioration is one of the main factors of , the grim situation of flood which is increasingly serious in that area. In 31 years (1954-1985), because of reclamation and silting, the area of the lake had been reduced to 66%, the total volume reduced to about 30%, and the flood storage had been reduced to about 60%, in addition to the drainage capacity reduced to about 60-70% in the high-water season, that’s caused by diked marshes, silt dunes, and reeds. The deterioration of East Taihu Lake also related to the rapid breeding of aquatic plants, and the eutrophication may arise. It is estimated that East Taihu Lake will be separated from the main body of Taihu Lake by 2000-2010, owing to the growth of Dongjiaozui silt dune, and as a result, the Taipu canal which is the main drainage project of Taihu Lake will lose its efficiency. A tentative idea of synthetical scheme including both engineering and ecological project is proposed.