Lake Baikal, located in the mountainous Russian region of Siberia, north of the Mongolian border, holds the title of the world's deepest lake. It reaches a maximum depth of approximately 1,642 meters (5,387 feet). Not only is it the deepest, but it is also considered the world's oldest lake, estimated to be around 25 million years old. Lake Baikal is a geological marvel, containing roughly 20% of the world's unfrozen surface fresh water, a volume exceeding all of the North American Great Lakes combined. Its extreme depth and age have created a unique ecosystem, often referred to as the "Galapagos of Russia," home to thousands of species of plants and animals, many of which are endemic and found nowhere else on Earth, such as the Baikal seal (nerpa), the only exclusively freshwater seal in the world.