One child was found dead and 13 others were hospitalized after a group of children and adults were found unconscious around a Quality Inn hotel's indoor pool in Niles, Michigan according to CNN.
Fire officials said they believe the cause was carbon monoxide poisoning.
Thirteen people were treated at local hospitals, including hotel staff members and first responders who helped unconscious victims.
Police said that, when they arrived, carbon monoxide levels at the hotel were 800 parts per million, according to WBND-TV.
US standards for carbon monoxide are 35 parts per million for a one-hour exposure.