Abstract: Remarkable changes in the structure of crustacean zooplankton took place in the Houhu region of Lake Donghu from the 1960s to 1990s: species numbers of cladocerans and copepods decreased from 47 to 17 and from 14 to 9, respectively. During this period, the dominant cladoceran Daphnia carinata ssp. was replaced by Diaphosoma brachyurum, population of Thermocyclops taihokuensis increased rapidly, while the calanoid Neodiaptomus yantsekiangensis and Neutroditapomus incongruens became very rare. With increased filter feeding fishes in the lake, the densities of cladocerans and calanoids decreased remarkably. The present result indicates that the decrease in species richness of crustacean zooplankton in Houhu region was mainly related to degradation of submersed vegetation, while the replacement of dominant crustacean species was mainly influenced by the changes in density of filter feeding fish.