Water diversion projects are currently an important means to improve lake water quality. However

the water diversion route

incoming water volume

and incoming water quality are all crucial factors to achieve the improvement. This study develops a two-dimensional hydrodynamic water quality model to simulate the hydrodynamic conditions of a lake area

and applies it in a case study of the Yangtze-to-Chaohu Water Transfer Project. Based on the shallow lake characteristics

we consider that water flow diverted into Chaohu Lake not only improves directly the lake water quantity

but may cause changes in the hydrodynamic conditions in the lake area and endogenous releases. Thus

this model simulates the impacts on water quality improvement caused by different water diversion routes and different water volumes that change the lake’s hydrodynamic conditions

by different incoming water quality

and by strong release of nitrogen and phosphorus from endogenous sources. The results show that water diversion imposes weak disturbances to the lake flow in wet years and strong ones in dry years. A larger diversion flow rate affects more the lake water quality. The incoming water quality is the key to determining whether or not the lake water quality can be improved. Overall

the water transfer affects less the water quality in the western lake area. In contrast

water quality in the eastern lake area is an indicator of the changes in water quality across the entire lake. A water diversion plan should be formulated based on the lake's real water volume and water quality status

and take into account the flow rate and water quality of the water diversion project.