Irtysh (Russian: Иртыш ; Kazakh: Ertis / Эртiс ; Tatar Cyrillic: Иртеш, Latin: İrteş ; 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 an the Altay Mountains.