Even with those precautions, cutting holes more than 10 inches in diameter in lakes in the Minneapolis park system violates Park Board ordinance and requires a permit, said spokeswoman Dawn Sommers. The board grants only one permit per year for such activity, for the Special Olympics to conduct a Polar Plunge on Bde Maka Ska.

“The person or entity altering the natural feature creates a liability, and therefore must assume the liability if someone were to become injured because of the alteration,” she said.

Sommers also added that fencing must be secure enough to keep people out of the hole when it is not being used, or guarded with 24-hour security. Park staff “has been trying to educate people on our ordinances, our permit processes, and the inherent dangers to ice bath users, as well as park visitors using the lakes for other activities,” Sommers said.

There was no immediate word on whether the Park Police might stop the popular dives. But Jewell said this weekend’s forecast bout of prolonged subzero temperatures certainly won’t.

“It will be a real challenge,” he said. “We have not had to deal with that yet.”