Grand Teton National Park WY – Grand Teton National Park officials are reminding boaters not to try “teak surfing” after two 9-year-old girls were hospitalized with carbon monoxide poisoning.

The girls were sickened Tuesday by a boat’s exhaust while trying the thrill sport in which swimmers cling to the back of a boat. They were on Jackson Lake with their parents and were taking turns holding onto a swim platform attached to the back of a 20-foot ski boat. The girls passed out and were hospitalized, but survived.

“Teak surfing” is illegal in many states and in all national parks. Grand Teton spokeswoman Jackie Skaggs says the accident is under investigation and that a citation may be filed in the case. A father of one of the girls was driving the boat.