Which river forms much of the boundary between Northeastern China and Far Eastern Russia?

The Amur River is the world's tenth longest river, forming the border between Far Eastern Russia and Northeastern China (Inner Manchuria). The largest fish species in the Amur is the kaluga, attaining a length as great as 5.6 metres (18 ft). The Amur River is the only river in the world in which subtropical Asian fish such as snakehead, coexist with Arctic Siberian fish, such as pike. The river is home to a variety of other large predatory fish such as Taimen, Amur Catfish, and yellowcheek.

The river rises in the hills in the western part of Northeast China at the confluence of its two major affluents, the Shilka River and the Ergune (or Argun) River, at an elevation of 303 metres (994 ft). It flows east forming the border between China and Russia, and slowly makes a great arc to the southeast for about 400 kilometres (250 mi), receiving many tributaries and passing many small towns. At Huma, it is joined by a major tributary, the Huma River. Afterwards it continues to flow south until between the cities of Blagoveschensk (Russia) and Heihe (China), it widens significantly as it is joined by the Zeya River, one of its most important tributaries.