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 and a drainage basin of 2,490,000 km². Permafrost underlies most of the catchment, 20% of which is continu…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 and a drainage basin of 2,490,000 km². Permafrost underlies most of the catchment, 20% of which is continuous.