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, 20% of which is continuous.