APPLETON, Wis. (AP) _ Wisconsin officials are warning about a new fad in which people, often teens, challenge others to jump into freezing water or else pay $100 to charity.

The fad took off about a month ago. It began spreading as jumpers posted cellphone videos to social media sites.

But the jumps aren't without risks. A 16-year-old Fond du Lac girl injured her knee jumping into Lake Winnebago, and a 16-year-old from Norwood Young America, Minnesota, died over the weekend after texting a friend he was about to do a cold-water challenge.

The Wisconsin Department of Natural Resources urges jumpers not to go alone, and to get out of the water quickly. The agency also advises wearing a life jacket and being very familiar with the area of water.