In what country is the Ob River?

The Ob River, also Obi, is a major river in western Siberia, Russia, and is the world's seventh-longest river. It forms at the confluence of the Biya and Katun Rivers which have their origins in the Altay Mountains. It is the westernmost of the three great Siberian rivers that flow into the Arctic Ocean (the other two being the Yenisei River and the Lena River).

The Ob forms 25 km (16 mi) southwest of Biysk in Altai Krai at the confluence of the Biya and Katun rivers. Both these streams have their origin in the Altay Mountains, the Biya issuing from Lake Teletskoye, the Katun, 700 kilometres (430 mi) long, bursting out of a glacier on Mount Byelukha.

The Ob's entire main course is within Russia, though its tributaries extend into Kazakhstan, China and Mongolia. The river splits into more than one arm, especially after joining the large Irtysh tributary at about 69° E. (Originating in China, the Irtysh is actually longer than the Ob from source to the point of their confluence.) From the source of the Irtysh to the mouth of the Ob, the river flow is the longest in Russia at 5,410 kilometres (3,360 mi). Other noteworthy tributaries are: from the east, the Tom, Chulym, Ket, Tym and Vakh rivers; and, from the west and south, the Vasyugan, Irtysh (with the Ishim and Tobol rivers), and Sosva Rivers.