Gaoyou Lake（）is the sixth largest freshwater lake in China, it is located between Anhui Province and Jiangsu Province. In a sense Gaoyou Lake is a manmade lake, and its creation is part of a long story about flood control and hydraulic engineering in ancient China. Gaoyou Lake is now part of the Huai River system as the Huai River flows south through Gaoyou Lake on its way to the Yangtze River and the Pacific. It is about 39 km long and 30 km wide, covering approximately 674.7 km².