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.

The Lena is a river in the Russian Far East, and is the easternmost of the three great Siberian rivers that flow into the Arctic Ocean. The Lena is the eleventh-longest river in the world, and the longest river entirely within Russia, with a length of 4,294 km (2,668 mi) and a drainage basin of 2,490,000 km2 (960,000 sq mi). Permafrost underlies most of the catchment, 77% of which is continuous.