A teenage boy visiting Yellowstone National Park was seriously burned when his foot broke through the ground near a geyser by the infamous Old Faithful, officials said.

It was the first known thermal injury in the park this year. Officials urged visitors to stay on designated boardwalks and trails in thermal areas.

The teenager, a 17-year-old boy, was hiking on Monday in the thermal area near the Lone Star Geyser, which is in the same geyser basin as Old Faithful, when his foot broke through the crust, causing “significant thermal burns to his foot and ankle area,” the park service said in a statement.