Reservoirs refer to artificial lakes, and smaller ones are called ponds, ponds and reservoirs. The general formation method is to dam the middle and upper reaches of the river, and the river will flood the valley to form a reservoir. However, some reservoirs are built at sea, such as Plover Cove Freshwater Lake in Hong Kong. Dams are usually built in narrow valleys, because the slopes on both sides can be used as natural walls of reservoirs, and the length of dams can be greatly shortened. Before construction, it is necessary to move the houses and historic sites in the flooded area to other places. The famous reservoirs in China are: Three Gorges Reservoir (the world's largest water conservancy project, the Three Gorges Dam, formed by intercepting the Yangtze River), Danjiangkou Reservoir (the water source of the Middle Route of South-to-North Water Transfer Project, the largest artificial lake in Asia), Xin 'anjiang Reservoir (Qiandao Lake in Chun 'an, Hangzhou, Zhejiang, a national 5A scenic spot), Wang Ying Reservoir (Yangxin Xiandao Lake in Huangshi, Hubei, a national 4A scenic spot) and Miyun Reservoir (the largest in North China).