| Lake Qiandaohu, located at the southwest edge of the Chinese most populated and economically developed Region, the Yangtze Delta, is one of the largest reservoirs in China. It has been playing a significant role in electric power generating, water supply, tourism, flood prevention and fishery etc., since its foundation in 1959. The lake ecosystem, not only serves as the underpinning to the regional social and economical development, but is also of great significance to assure the better environment quality and the water function of the mid-lower reaches of the Qiantangjiang River. The volume of L. Qiandaohu (176×10~8 m~3) is over 3 times as large as that of Lake Taihu, the Chinese third largest lake in the same region, though its surface area (583 km~2) is only about 1/4 of Lake Taihu. Thus water resources in L. Qiandaohu are becoming even more important, due to the widely water shortage faced in the region caused by poor water quality resulted from the increasing aquatic eutrophication. In addition, the lake ecosystem would inevasibly continue the ecological service such as pollutants purification etc. to the whole 10,442 km~2 drainage basin. So it is important to maintain and safeguard the health and stability of the lake ecosystem.In the recent decades, L. Qiandaohu, like most other lakes (and/or reservoirs) in China, has been continually challenged by the increasing influx of allochthonous nutrients, as the social development such as the rapid growth of human population, urbanization, and the development of both agriculture and industry. However, the stress of L. Qiandaohu by the increasing nutrients loading has been greatly reduced by the continual efforts paid by the local government and people through the control of point source of pollution and the shrinkage of non-point source of pollution by establishing forests round the lakes, which is quite different from most other lakes. It is these efforts that make the lake water quality to be continually maintained at the national surface water Class I.Unfortunately, even in such well-protected Lake Qiandaohu, a large algal (cyanobacterial) bloom had still repeatedly occurred in 1998 and 1999 and produced severe off-flavors to the water, which stimulated a wide concern for the better protection of lake environment and an urgent call for the exploration to the possiblecause of algal bloom and the corresponding technology of bloom control and prevention. The repeated outbreak of algal bloom also made the relationship between lake fishery development and aquatic environment protection to be the focus of dispute. "To be, or not to be", it was then a question for the lake fishery.In order to explore the cause of the rapid ecological deterioration of the lake ecosystem, and to find out a solution to harmonize lake fishery and environment protection, this study, based on historical data, made a scrutiny to all the blooming-related ecological factors and finalized a hypothesis to interpret the ecological mechanism of algal bloom occurred in the lake. This new interpretation of algal bloom mechanism, led us to the formulation of the theory, which we called aquatic environment protection oriented (AEPO) fishery, to develop lake fishery for the purpose of environment protection, that is, to improve the balance between top down and bottom up effects for the algae by stocking filter feeding Chinese carps, the silver carp and bighead carp for algal bloom prevention. We tested this theory by using an in-situ experiment in the lake in years. Meanwhile, due to the shortage of historical ecological study in the lake, a further ecological study on the basic chemophysical environment, and plankton community was carried out, especially the vertical variations of the major parameters were investigated, which not only supplied a gap to the ecological study of the lake, but also served as an evident of the effects resulted from the trial experiment of AEPO fishery in the lake. Besides, it would no doubt serve for the future research as historical reference data to the better understanding o...
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