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NORTHFIELD, Ill. — A suburban Chicago family is warning other parents about a day on the slopes that left them traumatized.

Melissa Mastros’ sons were skiing at Alpine Valley, a popular ski resort in Wisconsin, about 10 days ago when her 10-year-old lost control coming down one of the runs and fell. He tumbled through a small fence and into the river that runs through the resort. He briefly wound up tangled up in the fence underwater.

When she inquired about what had happened, Mastros learned it seems to happen a lot. A worker told her it happened at least twice that day.

“And she also told me coincidentally that someone else went in at 6 p.m. that night. And that’s kind of when an alarm went off in my head and I asked her how many people have been in that river, and she told me 20 or 25,” Mastros said.

It took a while to get her son out. His soaked ski boots weighed him down, and the water was deceptively deep. He was treated for hypothermia.

Outraged, Mastros threw a warning on Facebook and started hearing back from other parents with the same story. Some of them happened years ago. She said she can’t believe this has not been addressed.

“I think it’s disgusting,” she said, “I think it’s appalling. I think one person in that river is one too many, and the fact that they’re not doing anything about it is sick.”

Her son said he’s never going back, and other parents have said they don’t blame him.

Alpine Valley has not responded to request for comment.