Video narration
How can a region spread across northern Asia act like one drainage system? Think of a bathtub or sink: water moves downhill toward one outlet. The Northern Lowlands form a huge, roughly triangular expanse, reaching from northeastern Siberia westward toward the Ural Mountains and the Caspian Sea. Here's the key: the whole lowland slopes toward the Arctic Ocean. So the Ob, Yenisei, and Lena work as one northward-draining group. They carry the region's water into the Arctic Ocean.