Whats the "only mammal" would you find living in the world's "deepest lake"?

The world’s deepest lake is Lake Baikal in Russia. And you’ll find there the Baikal seal, Lake Baikal seal or nerpa. It is a type of earless seal widespread to Lake Baikal in Siberia, Russia and the only mammal there. Like the Caspian seal, it is interrelated to the Arctic ringed seal. The Baikal seal is one of the smallest true seals and the only completely freshwater pinniped species. It remains a scientific ambiguity of how the seals initially came to Lake Baikal, hundreds of kilometers from any ocean.