The Amur River (Russian: река Амур) or Heilong River (simplified Chinese: 黑龙江; traditional Chinese: 黑龍江) is a perennial river in Northeast Asia, forming the natural border between the Russian Far East and Northeast China (historically the Outer and Inner Manchuria). The Amur proper is 2,824 km (1,755 mi) long, and has a drainage basin of 1,855,000 km (716,000 sq mi). If including its main stem tributary, the Argun, the Amur is 4,444 km (2,761 mi) long, making it the world's tenth longest river.
The Amur is an important river for the aquatic fauna of Northeast Asia. The river basin is home to a variety of large predatory fish such as northern snakehead, Amur pike, taimen, Amur catfish, predatory carp and yellowcheek, as well as several species of trout and anadromous salmonids. The largest fish species in the Amur is the kaluga, a sturgeon that is one of the largest freshwater fish in the world, attaining a length as great as 5.6 m (18 ft). The Amur is also home to the northernmost populations of the Amur softshell turtle and Indian lotus.