Britannica Sources used in this answer

Why is the Ob-Irtysh river system longer than the Ob River alone?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Ob River The Ob and Yenisey river basins and their drainage networks.

The Ob-Irtysh river system is considered longer than the Ob River alone because the Irtysh River can be regarded as the main course of the river rather than merely its largest tributary.1

While the Ob proper, formed by the junction of the Biya and Katun rivers, has a course of 2,268 miles (3,650 km), the total length of the system reaches 3,362 miles (5,410 km) when measured from the source of the Black (Chorny) Irtysh in the Altai Mountains of China.1