Lake Baikal, Russia

The most voluminous freshwater lake in the world is Lake Baikal in Russia.  It is also among the clearest of all lakes, and thought to be the world's oldest lake at 25 million years. Baikal is home to more than 1,700 species of plants and animals, two thirds of which can be found nowhere else in the world and was declared a UNESCO World Heritage Site in 1996.