The Red River begins in China's Yunnan province in the mountains south of Dali. It flows generally southeastwardly, passing through ethnic minority areas before leaving China through Yunnan's . It enters Vietnam at . Once reaching the lowlands near Viet Tri, the river and its distributaries spread out to form the Red River Delta. The Red River flows pass the Vietnamese capital Hanoi before emptying into the Gulf of Tonkin.
Tonkin is the former name of the northern provinces of Vietnam and thus the eponymous body of water receiving the main river of "Tonkin".
The reddish-brown heavily silt-laden water gives the river its name. The Red River is notorious for its violent floods with its seasonally wide volume fluctuations. The delta is a major agricultural area of Vietnam with vast area devoted to rice. The land is protected by an elaborate network of dykes and .
In the 19th century, the river was thought to be a lucrative trade route to China. It was the forced opening of the Red River to European commerce that prompted the wars between France and the Vietnamese court , culminating in the conquest of Vietnam.
The and Lo River are the Red River's two chief tributaries.
*, administrative seat of Yuanyang County, Yunnan