Which lake is the oldest freshwater lake in the world?

Lake Baikal is the oldest freshwater lake in the world, with an estimated age of about 25–30 million years. It occupies an ancient active rift valley in southern Siberia, where Earth’s crust is slowly pulling apart.

Baikal is remarkable for more than its age. It is the world’s deepest lake, reaching 1,642 metres, and it holds about 22–23% of the planet’s unfrozen surface freshwater. Its great depth and volume make it the largest freshwater lake by volume, even though several lakes have larger surface areas.

The lake’s long geological history has allowed an unusually rich ecosystem to develop. Thousands of species live in and around Baikal, many of them endemic, including the Baikal seal, the world’s only freshwater seal species.

Lake Tanganyika is another ancient African rift lake and is often described as the world’s second-oldest lake. Lake Superior is much larger by surface area, but it formed far more recently through glacial processes.