With the exception of the delta of the Selenga, Lake Baikal is surrounded by lofty mountains.
It is certain that in previous geological ages Lake Baikal had a much greater extension.
The fauna, explored by Dybowski and Godlewski, and in 1900-2 by Korotnev, is much richer than it was supposed to be, and has quite an original character; but hypotheses as to a direct communication having existed between Lake Baikal and the Arctic Ocean during the Post-Tertiary or Tertiary ages are not proved.
Still, Lake Baikal has a seal (Phoca vitulina, Phoca baikalensis of Dybowski) quite akin to the seals of Spitsbergen, marine sponges, polychaetes, a marine mollusc (ancilodoris), and some marine gammarids.
The little Lake Frolikha, situated close to the northern extremity of Lake Baikal and communicating with it by means of a river of the same name, contains a peculiar species of trout, Salmo erythreas, which is not known elsewhere.