A dozen people are recovering after they were apparently sickened by carbon monoxide while boating on Lake Mead.
Park spokeswoman Christie Vanover said the incident was first reported about 8:30 a.m. Sunday.
Officials said five people were airlifted for treatment at University Medical Center, four were transported to the hospital by ground ambulance and three others were treated and released.
Vanover says it appears all the victims had been released from the hospital by Sunday afternoon.
She says the poisonous gas likely came from a generator on the boat.