The Dsmjiangkou Reservoir, consisting of Hanjiang reservoir area and Danjiang reservoir area, was built in 1968 with a volume of 1.7×10¹⁰ m³. It is a top-grade, multipurpose reservoir with functions of flood-control, electrcity-generation, navigation and agriculture. From Dec. 1992 to Sep. 1993, the floating crustaceans in the reservoir were surveyed for 4 times In order to rationally develop and make use of its fishery resources. The floating crustaceans in the reservoir are simple in species composition, including 36 species in 26 generas, among which 1 7 species in 11 genera are cladecera and 19 species in 15 generas copepoda. The standing crop is also low, 31.0 ind./L (or 0.6311 mg/L). The standing crop of cladecera is 6.6 ind./L(or 0.4504 mg/L), and that of copepoda 24.4 ind./L (or 0.1807 mg/L). Bosmina coregoni and Mescyclops leuckarii are the year-round dominant species. The species number of the floating crustacean reaches minimum in Dec., including 19 species and maximum in March, including 29 species. Individuals reach minimum (12.9 ind./L) in March and maximum (49.6 ind./L) in Sept.; biomass reaches minimum (0.3404 mg/L) in Dec. and maximum (1.2452 mg/L) in June. The mean individuals of the floating crustaceans at the sampling stations are 20.0 in Hanjiang reservoir area eind 14.8 in Danjiang reservoir area. The floating crustacean in the reservoir can support 5.87×10⁶ kg fish fed on floating crustacean every year.