Have you ever heard of something called secondary drowning? Parents are increasingly becoming aware of this little-known but very dangerous phenomenon, which can occur after a person inhales water into his or her lungs.

While incidents of secondary drowning are not common, it's important to know that it can happen even hours after a near-drowning or any incident during which some water suddenly enters the lungs (such as when kids jump into a pool or play on a water slide).

"Secondary drowning is rare but possible, so parents need to be vigilant," says Kristie Rivers, MD, a pediatrician at Bundoo, an online community for new and expecting moms run by physicians.

What is Secondary Drowning?

Secondary drowning can happen when a person suddenly takes water into the lungs. This can happen during a near-drowning event or while playing in the water--such as on a water slide--in such a way that water can quickly go into the lungs before a person has a chance to react.

What makes secondary drowning so scary is that the child or adult may seem fine after the incident, and may go hours before symptoms appear. But the water that entered the lungs can gradually cause swelling, or edema, and lead to breathing trouble and if left untreated, brain injury and even death.

Children are particularly at risk because they're less experienced in the water and are more likely to be focused on playing hard in the water than on safety. Younger children are also less likely to be able to tell you if something doesn't feel right.

What are the Symptoms of Secondary Drowning?

Here are some secondary drowning symptoms to watch for after any incident in which a child has inhaled water. If you see any of these symptoms, seek emergency medical help immediately.

• signs of respiratory difficulty such as breathing too fast or using stomach muscles to breathe
• lethargy, decreased energy, fatigue
• paleness
• audible crackling sounds when breathing
• wet-sounding cough

Remember to keep a close eye on your child since symptoms can appear hours later, even if a child seems fine initially after an incident in the water. In some cases, symptoms can appear as much as 24 hours after the event. "If your child was having a swimming lesson and went under the water that day, for instance, keep her in your room," says Dr. Rivers. "Even if a child was down for 20 seconds, she could have aspirated water into her lungs."

How to Prevent Secondary Drowning and Tips for Water Safety

The best way to prevent secondary drowning and pool drowning is to take steps to ensure water safety. Here are some pool safety tips for parents:

• Never leave a child alone to run and get something, even if it's just for a minute. "Have everything at arm's length," says Dr. Rivers.
   
• Make sure that you and your caregivers know CPR (cardiopulmonary resuscitation).
   
• Teach children--even older kids--to always ask permission before going in the water.
   
• Always supervise kids, even if they are good swimmers. Never be distracted when children are in the water. Try to avoid talking on the phone, socializing, or drinking alcohol, which can all take your attention away from the kids. With young children, make sure you have them within arm's reach.
   
• Teach kids to never play around drains, which can pose entrapment dangers.
   
• Teach kids to never play games in which they compete to hold their breath the longest.
   
• Instruct kids to never swim alone.
   
• Teach kids to never dive from the sides of the pool and only dive from the diving board.
   
• Keep toys away from the pool area when they are not being used.
   
• Never leave young children near water, even if it's a kiddie wading pool (a toddler can drown in as little as a few inches of water).
   
• If you own a pool, make sure it is completely fenced in with self-closing and self-latching gates that are out of the reach of small children.