Traditionally called a sea by local inhabitants, Lake Baikal is 636 kilometres (395 miles) long. Its exceptionally deep, crystalline waters are home to more than 1,200 creatures found nowhere else. The world’s only known freshwater seals, the nerpa, live in the lake. Towering mountains surround the lake, the oldest and deepest lake on the earth. While more than 300 rivers feed into Lake Baikal, the River Angara is the lake’s only outlet.