Irtysh (Russian: Иртыш ; Kazakh: Ertis / Эртiс ; Tatar: İrteş / Иртеш ; Chinese: Erqisi / 额尔齐斯河) a river in Siberia, the chief tributary of the river Ob. Its name means White River. It is actually longer than the Ob to their confluence. Irtysh's main affluent is Tobol River. The Ob-Irtysh form a major basin in Asia, encompassing most of Western Siberia and the Altay Mountains.
From its source as Kara-Irtysh (Black Irtysh) in the Mongolian Altay mountains in Xinjiang, China, Irtysh flows NW through Lake Zaysan, Kazakhstan until it meets the Ob near Khanty-Mansiysk in western Siberia, Russia after 4,248 km (2,640 mi).
Passenger, freight boats and tankers navigate most of the river between April and October, when it is not frozen. Omsk is home to the headquarters of the state-owned Irtysh River Shipping Company, and the largest river port in Western Siberia. Major hydroelectric plants at Ust-Kamenogorsk and Bakhtarminsk (1959) use the Irtysh near the Kazakhstan-Chinese border. An Irtysh-Karaganda irrigation canal supplies water to the dry Kazakstani Steppes.
The river banks were occupied by Chinese, Kalmyks, and Mongols until the Russians arrived in the late 16th century. The Russian conquest of the Irtysh basin was completed by the early 19th century.
The main cities on the Irtysh, from source to mouth, are:

in Kazakhstan: Öskemen/Ust-Kamenogorsk, Semey/Semipalatinsk, Pavlodar.
in Russia: Omsk, Tara, Tobolsk, Khanty-Mansiysk.