Irtysh River is the chief tributary of the Ob River. It flows northwest for 2,640 miles (4,248 kilometers) through China and Russia until it meets the Ob in western Siberia. Semipalatinsk, Omsk, and Tobolsk are the chief Russian cities on the Irtysh. Steamers can navigate most of the slow-moving river between April and November, when it is not frozen. Huge hydroelectric plants use the Irtysh near the Russian-Chinese border.
