Authorities say a father and two of his sons are lost in the swamps at Congaree National Park.
Department of Natural Resources officers say they heard the man yell for help Sunday, but they have not been able to pinpoint his location in the thick woods and swampy terrain. Authorities also don't know the condition of the boys, who are ages 6 and 10.
The father and sons were reported missing late Saturday night. Wildlife officers say they are near the River Trail, which cuts deep into the park down to the Congaree River.
Richland County deputies are helping park rangers in the search.