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The water quality of rivers flowing into lakes is a re-flection of the regional environment and significantly contributes to the nutrient levels of the lake.Based on multi-year monitoring data of the estuarine water quality of the Zi River which flows into the Dongting Lake,single factor analysis was performed for the dissolved oxygen,nitrogen ammonia(NH3-N),chemical oxygen demand,total phosphorus,permanganate index,and biochemical oxygen demand.The analysis indicated that the estuarine water quality class was dependent on the NH3-N level.The NH3-N trend of the Zi River was then simulated using an improved grey model IGM(0,N)based on a grey correlation analysis.The IGM(0,N)model produced a smaller average relative error and a more accu-rate prediction compared with a multiple regression model,thus validating the use of the IGM(0,N)model as a suitable method to simulate the estuarine water quality with a complex multi-factor system.