Great Lakes

The Great Lakes are a quintet of interconnected freshwater lakes in North America. They are Lakes Superior, Michigan, Huron, Erie, and Ontario. Superior, Michigan, and Huron are bigger than Lake Baikal, and are overall ranked 2nd, 4th, and 5th in the world respectively. Only the Caspian Sea is bigger.

The Great Lakes as seen from space.

Controversy

Nerpulation

Being large lakes that share the same latitude as the ringed seal, scientists have warned that if ringed seals ever wander into these waters, they could evolve over time, forming a third subspecies of ringed seal, joining Ladogas and Saimaas. Even worse, it could go further and speciate, giving us a second freshwater seal species, joining the world-infamous nerpas of Lake Baikal.

This could go beyond ringed seals: the Linkin Park Zoo in Chicago, close to the shores of Lake Michigan, is home to grey and harbor seals, meaning this process could apply to these two species as well.