Goose Creek, South Carolina (AP) A 10-year-old South Carolina boy has died several hours after he swallowed water in a swimming pool. Goose Creek police said Johnny Jackson swallowed some water while swimming around noon.

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 died at Trident Hospital.

Berkeley County Coroner Glenn Rhoad told the Post and Courier of Charleston the boy's lungs were filled with water and he died of asphyxiation. Rhoad said there was nothing suspicious about the death.

The tragic death focused a spotlight on the little-known phenomenon called "dry drowning" - and warning signs that every parent should be aware of.

"I've never known a child could walk around, talk, speak and their lungs be filled with water," Johnny's mother Cassandra Jackson told NBC News.

Jackson had taken her son to a pool near their home. It was the first time he'd ever gone swimming - and, tragically, it would be his last. At some point during his swim, Johnny got some water in his lungs. He didn't show any immediate signs of respiratory distress, and walked home with his mother and sister.

"We physically walked home. He walked with me," Jackson said. "I bathed him, and he told me that he was sleepy."

Later, she went into his room to check on him. "I walked over to the bed, and his face was literally covered with this spongy white material," she said. Johnny was rushed to a local hospital, but it was too late. Johnny had drowned, long after he got out of the swimming pool.