Goose Creek police say Johnny Jackson swallowed some water while swimming in a pool at his apartment complex around noon Sunday.
Police say he later complained he was tired and took a nap. When someone checked on him, water was coming out of his nose and he was having trouble breathing.
The boy later died at Trident Hospital.
Berkeley County Coroner Glenn Rhoad told the Charlestown Post and Courier of Charleston the boy's lungs were filled with water and he died of asphyxiation.