It’s fairly obvious why Lake Superior couldn’t support a blue whale type population. However, given that there are plenty of dolphins and porpoises in rivers and freshwater, and that there are seals that are isolated in lakes, most notably Baikal, but also several other isolated lakes, why are there no isolated cetacean populations in any lakes? Obviously seals can get on land a little better, but not really past the shoreline. Every dolphin could get to the ocean right now if it wanted to, but that’s not true for seals, how come?