Scientists studying the bears around the Beaufort Sea say this endurance swim could be a result of climate change, the BBC reported Tuesday.
Polar bears are known to embark on journeys between land and sea ice floes to hunt seals, but researchers say diminishing sea ice is forcing polar bears to swim greater distances, risking their own health and that of future generations.
Researchers from the U.S. Geological Survey published the details of their study in the journal Polar Biology.
"This bear swam continuously for 232 hours and 687 kilometers (426 miles) and through waters that were 2-6 degrees C (35 to 42 degrees F)," research zoologist George M. Durner said.
"We are in awe that an animal that spends most of its time on the surface of sea ice could swim constantly for so long in water so cold. It is truly an amazing feat."
Researchers say the epic journey, tracked with a GPS collar placed on the bear, came at a high cost for the animal.
"This individual lost 22 percent of her body fat in two months and her yearling cub," Durner said.
"This dependency on sea ice potentially makes polar bears one of the most at-risk large mammals to climate change."