Lake Baikal

The age of Baikal goes back to the oligocene.

An excerpt from the article 18 facts about Lake Baikal
The age of Baikal goes back to the oligocene. It is estimated that the lake exists about 25-30 million years. Its creation is associated with the collision of an Indian tectonic plate with Asia. It caused that the so-called the Amur plate began to move away from the Eurasian plate. A gap formed between them, which filled with water and thus Baikal arose.