Which river does the "water" of the South-to-North Water Transfer Project mainly refer to?

The "South-to-North Water Diversion Project" of the Yangtze River is a strategic project of People's Republic of China (PRC), which is divided into three routes: east, middle and west. The starting point of the East Line Project is located in Jiangdu Water Control Project in Yangzhou, Jiangsu Province. The starting point of the mid-line project is Danjiangkou Reservoir in the middle and upper reaches of the Han River, and the water supply areas are Henan, Hebei, Beijing and Tianjin. The conception of the engineering scheme was put forward in 1954 when President Mao Zedong visited the Yellow River. Since then, through the analysis and comparison of more than 50 schemes, the water transfer scheme has achieved many valuable results. The planning area of South-to-North Water Transfer Project involves a population of 438 million, and the water transfer scale is 44.8 billion cubic meters. [2] The total length of the east, middle and west trunk lines planned by the project is 4,350km. The first phase of the East and Middle Lines is 2,899 kilometers long, and the first-class supporting branch canals in six provinces and cities along the line are about 2,700 kilometers. From 2065438 to September 2002, the relocation of migrants in Danjiangkou reservoir area of the Middle Route of South-to-North Water Transfer Project was fully completed. The South-to-North Water Transfer Project mainly solves the problem of water shortage in northern China, especially in the Huang-Huai-Hai River Basin, with a population of 438 million. * * * There are three water transfer lines, namely the East Line, the Middle Line and the West Line, which are connected with the Yangtze River, the Yellow River, the Huaihe River and the Haihe River, forming an overall layout with "four horizontals and three verticals" as the main body, which is helpful to realize the rational allocation pattern of water resources in China. The Middle Route Project of South-to-North Water Transfer and the East Route Project of South-to-North Water Transfer (Phase I) have been completed, and water has been transferred to the northern region. Up to now, the west line project is still in the planning stage and has not started construction.