Argun /Аргунь

The Argun or Ergune (Chinese: 额尔古纳河) is a 1,620-kilometre (1,010 mi) long river that forms part of the eastern China–Russia border, together with the Amur. Its upper reaches are known as the Hailar River (海拉尔河) in China. The Argun marks the border (established by the Treaty of Nerchinsk in 1689) between Russia and China for about 944 kilometres (587 mi), until it meets the Amur.

Source: Wikipedia https://en.wikipedia.org/wiki/Argun_(Amur)