Transcript for Health Alert for Parents: Secondary Drowning
morning America" investigates and an important health alert for paerns as we start heading to beaches and pools this morning. There's a hidden danger, it's called secondary drowning that you may not know about. Here's bazi kanani. Reporter: He's an active child again after a pool party almost cost him his life. He had felt brave and jumped from the step into the spa. Reporter: The spa jets forced Rowan under water for at least 20 seconds before his mom was able to pull him out. He's okay. He's not blue. He's choking up the water. He seems fine. Reporter: An hour later, Rowan wasn't himself, he was lee that are jack. I called the doctor and he said to go to the E.R. Reporter: He was experiencing secondary drowning a condition that doctors say uncommon but say it can be fatal. 24 hours to develop symptoms. Most people if they have a significant event develop symptoms in 24 to 48 hours. Reporter: The fluid that remains in the lung prevents the tiny air sacs moving out to the lung. Decreased oxygen can cause the heart to stop. It takes a surprising small amount of fluid to actually cause damage to the lungs. In a child it can be a quarter of a can of a soda. Reporter: Rowan survived after a frightening stay in the hospital. She updated her blog, delighted momma, she's warning parents about the dangers of secondary drowning. Doctors say parents should keep an eye on their kids for up to 24 hours. If they have difficulty breathing, coughing, take them to the emergency room. At least a four-feet fence around your pool so they can't climb over. Reporter: Know what to do if your child goes under water. If they're unconscious, you need to immediately start cpr, have someone call the emergency services for you. Reporter: And when a child is in the water, someone needs to be watching all the time. I know now you can't turn your back five seconds. Reporter: For "Good morning America," bazi kanani, ABC news, Washington.
This transcript has been automatically generated and may not be 100% accurate.