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Lake eutrophication (LE) has become an increasingly severe environmental problem recently.However,there has been no nutrient standard established for LE control in many developing countries such as China.This study proposes a structural equation model to assist in the establishment of a lake nutrient standard for drinking water sources in Yunnan-Guizhou Plateau Ecoregion (Yungui Ecoregion),China.The modeling results indicate that the most predictive indicator for designated use-attainment is total phosphorus (TP) (total effect =-0.43),and chlorophyll a (Chl-a) is recommended as the second important indicator (total effect =-0.41).The model is further used for estimating the probability of use-attainment associated with lake water as a drinking water source and various levels of candidate criteria (based on the reference conditions and the current environmental quality standards for surface water).It is found that these candidate criteria cannot satisfy the designated 100％ use-attainment.To achieve the short-term target (85％ attainment of the designated use),TP and Chl-a values ought to be less than 0.02 mg/L and 1.4 tg/L,respectively.When used as a long-term target (90％ or greater attainment of the designated use),the TP and Chl-a values are suggested to be less than 0.018 mg/L and 1 μg/L,respectively.