A new study has some more bad news for polar bears.

Polar bears need sea ice in order to rest after a long hunt in the water for seals and other prey, but as global warming lowers ice levels, there is less and less sea ice every year, according to a Zoological Society of San Diego statement.

Scientists recently tracked the movements of polar bears in the Beaufort Sea and Hudson Bay and found that the bears were swimming much greater distances than they had in the past, indicating that it’s getting harder and harder for them to reach sea ice.

Although Arctic sea ice typically disappears in the summer, a lot more of it is melting than before, and it’s continuing to shrink as global warming and climate change take their toll.

Arctic sea ice dropped to a record low in 2012, and a majority of adult females in that year logged at least one swim longer than 31 miles in the Beaufort Sea. That’s quite a long way to swim even for polar bears, which are excellent swimmers. Although they can manage such a distance, it means they have to burn more precious calories, meaning they have to hunt more as well.

“Recent studies indicate that swimming may be energetically costly to polar bears,” said Nicholas Pilfold, postdoctoral fellow at San Diego Zoo Global, in the statement. “Given the continued trend of sea ice loss, we recognize that an increased frequency in the need to engage in this behavior may have serious implications for populations of polar bears living around the Arctic Basin.”