Abstract:

The water quality and the structure and amount of algae phytoplankton in Lake Gaoyou were investigated and the trophic status was determined by comprehensive eutrophication state index,singlefactor phytoplankton index and Margalef index.The results showed pH average was 866,DO average was 73 mg/L,TN average was 1.02 mg/L,TP average was 0051 mg/L,CODMn average was 961 mg/L,Chla average was 1038 ug/L,SD average was 0.69 m.66 species belonged to 38 genera,23 families,8 phyla were found in Lake Gaoyou,of which 27 species belong to Chlorphyta，16 species belong to of Cyanophyta,9 species belong to Bacillariophyta and 6 species belong to Euglenophyta,and  the percentage of them were 4091%,2424%,1364% and 909%.The average density and biomass of phytoplankton were 1940×106 ind./L and 483 mg/L.The comprehensive nutrition state index was between 5114 and 6053.The phytoplankton community structure was of greenblue agale type and Margalef index was 1528.All the features indicated that the lake can be regarded as light eutrophication and there was the tendency of middle eutrophication.〖 〖W