Updated

A fad in which people challenge their friends to jump into freezing water in efforts to raise money charity has prompted warnings from state and school officials across the nation.

The phenomenon began last month as a fundraiser for a 6-month-old cancer patient in Missouri. As it spread on social media, the rules about contributing to charity evolved into several variations.

As the so-called cold-water challenges have grown, more divers have reported broken bones, blown-out knees or worse. They might misjudge the water's depth or land on a submerged object.

High schools in Illinois, Minnesota and Wisconsin have begun alerting parents to the practice. State officials are urging divers to use extreme caution.

However, one Indiana cancer charity says the phenomenon helped it raise $1,500 in a month.