Ob

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Ob River in w Siberia, central Russia. It flows nw then ne through the lowlands of w Siberia, before continuing n and then e to enter the Gulf of Ob, an arm of the Kara Sea within the Arctic Ocean. Length: 3680km (2300mi). With its principal tributary, the Irtysh, it is the seventh-longest river in the world: 5410km (3360mi).