The physicochemical and biological characteristics of water were studied from 2001 to 2004 in Shuikou impoundment. The results showed ： The growth of Water Hyacinth (Eichhomia crassipes) and Water Lettuce (Pis-tia stratiotes) caused the increase of concentrations of transparency、nitrate、ammonium、total nitrogen、total phosphorus and total bacteria, the decrease of the values of pH,DO,permanganate index、total plankton and species Diversity of plankton reduced, step toward miniaturization of plankton volume.