By day and night, each participant took four one-hour shifts, without a wetsuit — dealing with the cold, six-foot waves, and little sleep.

The swimmers were watched over carefully by crews in kayaks, sailboats and zodiacs.

Experts say a swim like this might not have been possible just a few decades ago.

“We’re in an era now where we have many more years where it would be tolerable, and fewer and fewer where it would be told cold to do this,” says Jay Austin, a U of M Duluth physics and astronomy professor who’s also been studying about changes in Lake Superior.

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