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How does the Ob River rank among the worldâs longest rivers when the Irtysh is included?
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Ob River
The Ob and Yenisey river basins and their drainage networks.
When the Irtysh River is considered part of the main course rather than just a tributary, the Ob River system is ranked as the seventh longest river in the world.12
This combined system, referred to as the ObâIrtysh, reaches a total length of approximately 5,410 kilometers (3,362 miles), measured from the source of the Black Irtysh in the Altai Mountains of China.12