The Amur River or Heilong River is a perennial river in Northeast Asia, forming the natural border between the Russian Far East and Northeast China. The Amur proper is 2,824ย km (1,755ย mi) long, and has a drainage basin of 1,855,000ย km2 (716,000ย mi2). If including its main stem tributary, the Argun, the Amur is 4,444ย km (2,761ย mi) long, making it the world's tenth longest river.