The Irtysh is a river in Russia, China, and Kazakhstan. It is the chief tributary of the Ob and is also the longest tributary river in the world.

The Ob is a major river in Russia. It is in western Siberia, and with its tributary the Irtysh forms the world's seventh-longest river system, at 5,410 kilometres (3,360 mi). The Ob forms at the confluence of the Biya and Katun which have their origins in the Altai Mountains. It is the westernmost of the three great Siberian rivers that flow into the Arctic Ocean. Its flow is north-westward, then northward.