The “Sea Bear”, (Ursus maritimus) commonly referred to as a Polar bear are considered marine mammals. With three to four inches of blubber for buoyancy and massive 12” forepaws these bears are excellent swimmers.
No-one really knows their limits but they have been known to swim more than 60 miles without a rest.

To look at the Sea Bear they appear white. Despite what we perceive their fur is not white, each hair shaft is pigment-free and transparent with a hollow core. They look white because the hollow core scatters and reflects the visible light. The result of this hollow core is an insulation so efficient that no perceptible heat escapes. When looked at through infrared their presence cannot be detected except for minute traces of their breath. Adding their fat layer to this air tight insulation can make an adult Polar bear overheat quickly when running. Not that this will do you any good if attacked, because they will out run you.