The Baikal seal lives only in the waters of Lake Baikal.[6] It is something of a mystery how Baikal seals came to live there in the first place. They may have swum up rivers and streams or possibly Lake Baikal was linked to the ocean at some point through a large body of water, such as the West Siberian Glacial Lake or West Siberian Plain, formed in a previous ice age. The seals are estimated to have inhabited Lake Baikal for some two million years.[7]