The hydrodynamic effects of reconnecting a lake group with the Yangtze River were simulated using a three-dimensional hydrodynamic model.The model was calibrated and validated using the measured water temperature and total phosphorous.The circulation patterns,water temperature,and water exchange conditions between sub-lakes were simulated under two conditions:(1) the present condition,in which the lake group is isolated from the Yangtze River; and (2) the future condition,with a proposed improvement in which connecting the lake group with the Yangtze River will allow river water to be diverted into the lake group.The simulation period selected was characterized by extremely high temperature and very little rain.The results show that the cold inflow from the river has a significant effect on the water temperature only near the inlets,and the effect is more obvious in the lower water layers than that in the upper ones.The circulation pattern changes significantly and small-scale vortices only exist in part of the lake regions.The water exchange between sub-lakes is greatly enhanced with the proposed improvement.The water replacement rate increases with water diversion but varies in different sub-lakes.Finally,a new water diversion scheme was proposed to avoid contamination of some lakes in the early stage.