The Hai River, previously called Bai He, is a river in the People's Republic of China which flows through Beijing and Tianjin before emptying into the Yellow Sea at the Bohai Gulf. The Hai River at Tianjin is formed by the confluence of five rivers, the Southern Canal, Ziya River, Daqing River, Yongding River, and the Northern Canal. The southern and northern canals are parts of the Grand Canal. The Southern Canal is joined by the Wei River at Linqing. The Northern Canal joins with the Bai He (or Chaobai River) at Tongzhou. The Northern Canal is also the only waterway from the sea to Beijing. Therefore, early Westerners also called the Hai He the Bai He.
At Tianjin, through the Grand Canal, the Hai connects with the Yellow and Yangtze rivers. The construction of the Grand Canal greatly altered the rivers of the Hai He basin. Previously, the Wei, Ziya Yongding and Bai Rivers flowed separately to the sea. The Grand Canal cut through the lower reaches of these rivers and fused them into one outlet to the sea, in the form of the current Hai He. Hai He is 1,329 kilometres (826 mi) long measured from the longest tributary. However, the Hai He is only around 70 kilometres (43 mi) from Tianjin to its estuary. Its basin has an area of approximately 319,000 square kilometres (123,000 sq mi). Its annual flow is only half that of the Yellow River, or one-thirtieth that of the Yangtze River.