The Sayan Mountains are a mountain range between northwestern Mongolia and southern Siberia, Russia. The Eastern Sayan extends 1,000 km (621 mi) from the Yenisei River at 92° E to the southwest end of Lake Baikal at 106° E. The Western Sayan forms the eastern continuation of the Altai Mountains, stretching for 500 km (311 mi) from 89° E to the middle of the Eastern Sayan at 96° E. The Sayan Mountains' towering peaks and cool lakes southwest of Tuva give rise to the tributaries that merge to become one of Siberia's major rivers, the Yenisei River, which flows north over 2000 miles to the Arctic Ocean. This is a protected and isolated area, having been kept closed by the Soviet Union since 1944.