Ob

Major river in Asian Russia, flowing 3,380 km/2,100 mi from the Altai Mountains through the western Siberian Plain to the Gulf of Ob in the Kara Sea (an inlet of the Arctic Ocean). With its main tributary, the Irtysh, the Ob is 5,600 km/3,480 mi long, and drains a total area of 2,990,000 sq km/1,150,000 sq mi.

Although frozen for half the year and subject to flooding, the Ob is a major transport route. It is chiefly used for transporting the natural gas and oil extracted in the region, along with timber, grain, peat, and coal. Novosibirsk and Barnaul are the main ports on its banks.

The headstreams in the Altai that form the Ob are the Katun and Biya. The river is very wide and sluggish for most of its course, and in its middle reaches flows through extensive marshland. As it approaches the Kara Sea, it fans into a delta covering some 4,000 sq km/1,544 sq mi. The main tributaries, apart from the Irtysh, are the Tom and the Chulym. Several hydroelectric power schemes, such as that at Novosibirsk, have been constructed on the river. The Ob region was first charted by explorers from Novgorod in the 11th century, but was not colonized until the late 16th century.