Amur (ämŏrˈ) [key], Chin. Heilongjiang, river, c.1,800 mi (2,900 km) long, formed by the confluence of the Shilka and Argun rivers, NE Asia, at the Russian-Chinese border; the Amur-Shilka-Onon system is c.2,700 mi (4,350 km) long. The Amur flows generally southeast, forming for more than 1,000 mi (1,610 km) the border between Russia and China, then NE through Russia before entering the Tartar Strait opposite Sakhalin island. Its chief tributaries are the Ussuri, Songhua, Zeya, and Bureya rivers. One of the chief waterways of Asia, the Amur is navigable for small craft for its entire length during the ice-free season (May–Nov.). The chief ports are the Russian cities of Khabarovsk (the head of large craft navigation), Komsomolsk, and Nikolayevsk.