By using enclosure method,the Microcystis bloom which disappeared after 1985 in Donghu Lake (Wuhan, China) was successfully recovered, and some causal factors of the resumption and disappearance of the summer Microcy at is bloom were dealt with.According to the biomanipulation theory, the authors designed a series of stocking experiments in which three domestic fishes-silver carp, bighead carp and grass carp were introduced.The results show that in the silver carp and bighead carp stocking enclosures, the bloom vanished in a short period (15 days), and no change took place in the grass carp stocking enclosures, whereas in the fish-free enclosures, the bloom was even more abundant.It is concluded that planktivorous fish have great effects on the plankton community structure of the enclosures where Aficrocy bloom occurred.Also, the fluctuation of various forms of carbon, nitrogen and phosphorus were fully discussed in order to show some implications of their effects on Microcy stis bloom.