River, western Russia.
Flowing across western Siberia northwestward from the Altai of central Asia, it courses through the Gulf of Ob into the Kara Sea of the Arctic Ocean. It is about 2,268 mi (3,650 km) long. Its middle course is through taiga , swampy coniferous forest with expanses of marshland. In the north are vast stretches of icy, treeless tundra . The Ob is an important source of hydroelectric power and one of Siberia's major transportation routes during the six months of the year when it is not frozen.