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Lake eutrophication is one of the most important and harmful environmental problem and thus brings a tremendous influence on sustainable development of society and economy in lake regions.Eutrophication is defined as the enrichment of surface waters with nutrient.Of these nutrients nitrogen (N) and phosphorus (P) are important influence factors.Poyang Lake is the biggest freshwater lake in China,and itswater quality is good among the five biggest freshwater lakes.But it has been observed with accelerated nutrient enrichment in the past two decades.The concentrations of nitrogen and phosphorus were measured in the lake water and the major tributaries river water of Poyang Lake.And the state of trophic in Poyang Lake water was analyzed.The results showed that the Poyang Lake is facing eutrophication with high nutrients and the nitrogen and phosphorus is the main nutrient elements,and the nitrate nitrogen dominated in the forms of nitrogen in Poyang Lake,The loads of nitrogen were very high in Poyang Lake water,and the ratio of N/P more than 7.It will appear eutrophication phenomena if the suitable conditions were met.The state of eutrophication is dissimilar at different season.It is already in the eutrophic state at low and average water period,and is in the meso-eutrophic state at high water period.