It's not like they breathe through gills. They breathe through a blowhole when they surface.
It's not like they breathe through gills. They breathe through a blowhole when they surface.
But their skin, their blood, and their body chemistry are all adapted to constant contact with salt water. I find it difficult (but not impossible, if there's someone around with actual expertise) to believe that none of that would be thrown off in a fresh-water environment.