By Brad Edwards

(CBS) — A new trend has teenagers from New Trier High School taking a dangerous plunge called the “cold water challenge,” with students nominating each other to jump into Lake Michigan.

New Trier officials sent an email to parents warning them about the dangers.

“While this may seem like harmless fun, we believe it is a safety concern. A few students already have been injured while jumping into shallow water from rocky shorelines,” the statement said.

The rocky shorelines just east of the high school campus are especially dangerous because there’s no way to tell what’s beneath the surface.

Plus, the water is very cold. Friday temperatures were 37 degrees.

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