West Siberian Glacial Lake

The West Siberian Glacial Lake, also known as West Siberian Lake (Западно-Сибирское море) or Mansiyskoe Lake (Мансийское озеро, Mansi Lake), was a periglacial lake formed when the Arctic Ocean outlets for each of the Ob and Yenisei rivers were blocked by the Barents-Kara Ice Sheet during the Weichselian Glaciation, approximately 80,000 years ago. It was situated on the West Siberian Plain, and at its maximum extent the lake's surface area was more than 750,000 km2 which is more than twice that of the present-day Caspian Sea.

It is theorized that although drainage to the Arctic Ocean basin (e.g. by the Ob and Yenisei Rivers) was prevented, the lake would eventually overflow to the Mediterranean Sea through a circuitous route that would include the Aral Sea, the Caspian Sea, and the Black Sea. This would have resulted in water from the Selenga River and Lake Baikal draining over a course of some 6000 mi, considerably longer than any river's course today.

See Mangerud et al. (2004) for diagrams and descriptions of the lake as well as postulated drainage patterns.