West Siberian Glacial Lake

The West Siberian Glacial Lake, also known as West Siberian Lake (Russian: Западно-Сибирское море) or Mansiyskoe Lake (Russian: 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.

Source: Wikipedia — West Siberian Glacial Lake (CC BY-SA 4.0)