According to Official Guinness Records,
Lake Baikal, Siberia, Russia, is between 20 and 25 million years old, and was formed as a result of a tectonic rift in the Earth's crust. The rift is very much active and is causing Baikal to continue to widen at an approximate rate of 2 cm (0.7 in) per year. It holds more water than all of North America's Great Lakes combined and is host to a wealth of biodiversity, including the world's only freshwater seal.
For a complete list of Unknown date records, please visit Unknown date Guinness Records in Russia.