WARMING: Retreating sea ice is blamed for what could be a long and dangerous swim.

Federal wildlife monitors spotted nine polar bears in one day swimming in open ocean off Alaska's northwest coast, and environmental groups say the event is a strong signal that diminished sea ice brought on by warming has put U.S. bears at risk of drowning or dying from effects of fatigue.

"The impact of global warming is brutal and tragic for polar bears," said Kassie Siegel of the Center for Biological Diversity. "The only way to limit the number of bears that will drown and starve is to reduce greenhouse gas pollution immediately."

The number spotted Saturday on long-distance swims in the Chukchi Sea was higher than has been seen in similar surveys.

Polar bears spend most of their lives on sea ice, which they use as a platform to hunt their primary prey, ringed seals. Polar bears are powerful swimmers, but are at increased risk of drowning in high wind and rough seas, Siegel said.

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