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 (sharing a channel with Bai He) 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.
The Hai River is 1,329 kilometers (826 mi) long measured from the longest tributary. However, the Hai River is only around 70 kilometers (43 mi) from Tianjin to its estuary. Its basin has an area of approximately 319,000 km2 (123,000 sq mi).