On: The fish kick may be the fastest subsurface swim stroke yet (2015)

[ethan_smith]

Bears, particularly polar bears, are terrestrial mammals with impressive swimming capabilities - they can swim up to 60 miles without rest and use a modified dog paddle that's remarkably efficient.

[seszett → ethan_smith]

To be precise though the species is called Ursus maritimus and it is often considered a semi-aquatic species rather than just a terrestrial mammal.