Drinking water crisis caused by blue algal bloom in Lake Taihu in Wuxi in May in 2007 presented austere situation of lake eutrophication and bloom in China. Based on the analysis of the eutrophication development, the cause and mechanism of bloom, the approach and measurement of lake eutrophication and control are presented. The serious eutrophication and extremely difficult lake control in Lake Taihu are attributed to the following three causes. Firstly, Lake Taihu is located in floodplain of the middle and lower reaches of the Yangtze River with high trophic history. Secondly, frequent appearance of bloom is related to the physiological advantage of cyanobacteria including fixture of carbon dioxide, vacuole for moving towards the radiant energyrich zone, characteristic light absorption and the utilization of nutrients. Finally, bloom is related to the physical, chemical and biologic environment of ecosystem such as particular underwater light climate and low predation pressure. For the control of eutrophication, people should follow the sequence from pollution sources control, ecological restoration to catchment management. Permeable dam and wetland techniques to control external pollution, physical and biological techniques to control the internal nutrient release, and submerged aquatic vegetation restoration could be selected. The control techniques of algal bloom include the physical (enclosure), chemical (flocculation) and ecological (ecological floating bed and biomanipulation) engineer methods. For a specific lake, applicable lake harness techniques should be selected based on the distinct ecosystem types and environmental problems.