The Argun or Ergune () is a long river that forms part of the eastern China–Russia border, together with the Amur. Its upper reaches are known as the Hailar River () in China. The Argun marks the border (established by the Treaty of Nerchinsk in 1689) between Russia and China for about , until it meets the Amur.
Name
The name derives from Buryat Urgengol 'wide river' (urgen 'wide' + gol 'river'). Mongolian word "ergün" (in Traditional Mongolian alphabet) or "örgön" (in modern Mongolian) means "wide".
Geography
The river flows from the western slope of the Greater Xing'an Range in China's Inner Mongolia, and forms the Chinese side of the two rivers that flow together to produce the Amur (Heilong). Its confluence with the Shilka at Ust-Strelka on the Russian side forms the Amur. The Argun is long including its upper course Hailar, and has a drainage basin of . Its main tributaries are the Urov, Uryumkan and Gazimur from the left, and the Gen He from the right.