By the analysis of water quality monitoring data of Dongting Lake watershed in 1989

1997 and 1999

it indicated that phosphorus pollution was particularly heavy

but the highest concentration of the heavy metals except Cu in each yearwas all lower than statewater quality standard grade Ⅱ;water pollution levels increase year after year at a high rate

except contam ination TN;point sources make a greater contribution to the pollution of Dongting Lake watershed and concentrations of the contam inates are higher in low water season than in high water season and tap water season. Due to the shortage of research on toxicity harmfulness coefficients of TN and TP

their values are obtained through an extrapolation approach using toxicity coefficients of heavymetals determ ined abroad. The coefficients are applied furthermore to risk analysis of pollution in Dongting L akewatershed. The research results show that TP contributesmost to the pollution risk in Dongting L ake watershed

while TN and Zn contribute relatively less.A dditionally

the risk coefficient value at Junshan monitoring site is relatively high

which poses potential ecological risk for its circum ference ecosystem.The risk values at other monitoring sites are lower and the potential ecological harm is minimal .