Little known swimming safety risks

Most of us tend to think that drowning accidents only occur when a person struggles in deep or rough waters and isn't rescued in time. But it can also happen in some unexpected ways, and the signs are not always what people expect. In rare cases a swimmer can experience trouble breathing and even die hours after a seemingly successful rescue.

Every year, more than 3,500 Americans die from unintentional drowning, according to the Centers for Disease Control and Prevention. Typically, children are at highest risk; approximately 1 in 5 drowning victims are children 14 and younger.

Though relatively uncommon, it's important to be aware of two types of health risks that may occur in the aftermath of a close call at the beach or pool.

"It is an unusual phenomenon," Dr. Holly Phillips told "CBS This Morning." "Basically there are two forms of out-of-water drowning. The first one is called dry drowning. That's after maybe they've had a struggle in the pool, you've inhaled a little water. It creates irritation in your airway. That causes muscle spasms, so you start to choke and you have trouble breathing."

Similarly, after a drowning incident, there can be a build up of fluid in the lungs, which may cause the person to have trouble breathing, a condition known as secondary drowning.

"It can happen up to 24 hours after you're already out of the pool and what's happened is you've inhaled some water," explained Phillips. "Usually, again, it's after a bit of a struggle and it irritates the lung tissue itself and causes inflammation of the lung tissue and starts to make fluid and creates something called pulmonary edema. So the lungs themselves create the fluid and you're drowning even though you're not in the water."

Dry drowning and secondary drowning -- which only account for about 1 to 2 percent of all drowning deaths -- may result in long-term respiratory problems or brain damage, and can be fatal if left untreated.

This is why it's important to keep an eye on a near-drowning victim for some time after they've been safely brought to shore. A person who survives a drowning incident may later exhibit shortness of breath, chest pain and cough, as well as extreme fatigue and mood changes. If any of these symptoms emerge, it's important to see a doctor right away. Both dry drowning and secondary drowning can be treated with oxygen and ventilation at an emergency room. If caught early, a patient is likely to recover.

"It's something we have to know about because it's easy to miss, especially in kids," said Phillips. "They're playing in the water, you might not see a struggle and frankly they could be irritable and have fatigue after swimming anyway. You might not know to look for it."

Another little known risk parents should be aware of is that young children don't need to be in a large body of water to drown. Young kids can drown even in shallow water -- as little as two inches of water is all it takes, experts say. This is why it's never safe to leave a child unsupervised in or near the pool, beach or bathtub.

Many people don't realize that someone who is drowning may not exhibit typical signs such as flailing their arms, splashing and struggling to stay above water. Often a drowning person slips quietly beneath the surface without drawing the attention of people nearby.

Shallow blackout syndrome, another scary and little known risk associated with water recreation, can happen to even the strongest and most experienced swimmers, and often without warning.

Shallow blackout syndrome occurs when a person takes in several deep breaths -- also known as hyperventilation -- before heading under water, perhaps when attempting to swim the length of a pool. Holding deep breaths under water lowers the body's carbon dioxide levels, which suppresses the breathing reflex and causes a swimmer to lose consciousness when oxygen levels fall below a certain threshold. It's important for parents to advise children not to compete with peers to see who can hold their breath longest. Swimming instruction usually addresses the issue of safe breathing.

Thankfully, many of these risks are preventable, and it starts with basic water safety. If you or your child does not know how to swim, it's important to learn before taking a dip in the ocean or hopping in the pool. And part of learning how to swim is knowing what to do when you're in a situation that feels unsafe or scary, which is common for new swimmers, especially at the beach.

Dr. Antonio Dajer, director of the emergency department at the New York-Presbyterian hospital campus in Lower Manhattan told CBS News that anyone who wades into the ocean should know what to do in case they encounter a strong current or riptide. "Just let it ride out, don't fight it, just float out," he said. "Stay floating and you'll be fine. But when you start thrashing and panicking you will not do well. People are surprised that they're so close to shore and it's powerful."

The American Red Cross offers tips for safe swimming, as well as resources to help you find swimming and water safety classes in your area.