Some of Mongolia's waterways drain to the oceans, but many finish at Endorheic basins in the deserts and the depressions of Inner Asia. Rivers are most extensively developed in the north, and the country's major river system is that of the Selenge, which drains via Lake Baikal to the Arctic Ocean. Some minor tributaries of Siberia's Yenisei River, which also flows to the Arctic Ocean, rise in the mountains of northwestern Mongolia. In northeastern Mongolia the Onon River drains into the Pacific Ocean through the Shilka River in Russia and the Amur (Heilong Jiang) rivers, forming the tenth longest river system in the world.