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I used to be a big fan of the novels written by John Irving. One of my favorites was The World According to Garp. There was a scene where the main character, Garp, took his two young sons to the beach. To his youngest he warned, "Be careful of the undertow" but to the boy's ear he heard "undertoad" and thus assumed that there was some large, long-legged amphibian lying in wait to gobble him up just beyond the surf line. That misunderstanding served as a metaphor later in the book whenever bad things started happening.

Of course, undertow is an incorrect way of referring to what's known as a rip current, a dangerous phenomenon which has been in play at Lowcountry beaches lately. So far this season it's reported that 21 people have been rescued from rip currents with three of those incidents classified as near drownings. In fact, the United States Lifesaving Association estimates that the annual number of deaths due to rip currents on our nation's beaches exceeds 100. Rip currents account for over 80 percent of rescues performed by surf beach lifeguards.

It was back in my mid-teens that I had a frightful experience with a rip current. I was attempting to swim out to a sandbar, realized it was too far and started swimming back to shore. That's when I realized I was being flushed out to sea and started to panic. I guess it was teenage pride or that teenage sense of indestructibility, but I didn't dare yell out for help. Fortunately, another kid on a raft was paddling out to the sandbar right towards me and I simply asked if I could hang on his raft to rest a little. As is usually the case, rip currents tend to form around sandbars, something I've always been aware of but never really completely understood.

Rip currents are born out of ordinary, everyday ocean waves. Some external force (typically the wind) pushes on the ocean, creating a swell of water, which is passed along the ocean's surface. Eventually, some waves meet up with land. In areas with a rocky shore, the water surge "crashes" as it is deflected. On a sandy beach with a gently sloping shore, the swell simply pushes uphill. The climb up the beach drains all the energy of the surge, and the water eventually flows downhill, back to the ocean -- in other words, the water finds its own level again. Ordinarily, this receding flow of water moves with little force. The slight slope of the beach effectively spreads out the force over a great distance so it's not particularly strong at any one point. And since it's weaker than the opposing force of incoming waves, the receding flow usually won't carry you out to sea.

A rip current occurs when the receding flow becomes concentrated in a particular area at a particular time. There are a number of things that can cause this, but the most common is a break in a sandbar. Sandbars are long, narrow hills of accumulated sand along the outer part of the shore. They are formed by the motion of waves and tides. When a large sandbar forms, it can produce a sort of basin along the ocean shore. Waves move up against the sandbar with enough force to push water into the basin but the receding water has a hard time making it back over the sandbar to return to sea. This is something like a bathtub with the drain plugged up. Just as the water in a bathtub is being pulled downward by gravity but is blocked by the drain plug, the receding wave is being pulled outward by the ocean (and by gravity) but is kept in by the sandbar. In some cases, the backward pressure of the receding water may be strong enough to break through part of the sandbar.

Other times, the water flows along parallel to the beach until it reaches a low point on the sandbar. In either case, the water that has piled up in the basin rushes out to sea once it finds an opening, just as the water in your bathtub rushes out when you unplug the drain. The resulting rip current sucks in water from the basin and spits it out on the other side of the sandbar. Rip current speeds are typically one to two feet per second. However, speeds as high as eight feet per second have been measured--this is faster than an Olympic swimmer can sprint so rip currents can sweep even the strongest swimmer out to sea.

Some of the telltale signs that a rip current is present:

-a channel of churning, choppy water

-an area having a notable difference in water color

-a line of foam, seaweed, or debris moving steadily seaward

-a break in the incoming wave pattern

The NOAA rip current website advises the following:

-Whenever possible, swim at a lifeguard-protected beach.

-Never swim alone.

-Learn how to swim in the surf. It's not the same as swimming in a pool or lake.

-Be cautious at all times, especially when swimming at unguarded beaches. If in doubt, don't go out.

-Obey all instructions and orders from lifeguards. Lifeguards are trained to identify potential hazards. Ask a lifeguard about the conditions before entering

the water. This is part of their job.

-Stay at least 100 feet away from piers and jetties. Permanent rip currents often exist along side these structures.

-Consider using polarized sunglasses when at the beach. They will help you to spot signatures of rip currents by cutting down glare and reflected sunlight off the ocean's surface.

-Pay especially close attention to children and elderly when at the beach. Even in shallow water, wave action can cause loss of footing.

If caught in a rip current:

-Remain calm to conserve energy and think clearly.

-Never fight against the current.

-Think of it like a treadmill that cannot be turned off, which you need to step to the side of. Swim out of the current in a direction following the shoreline. When out of the current, swim at an angle--away from the current--towards shore.

-If you are unable to swim out of the rip current, float or calmly tread water. When out of the current, swim towards shore.

-If you are still unable to reach shore, draw attention to yourself by waving your arm and yelling for help.

If you see someone in trouble, don't become a victim too:

-Get help from a lifeguard.

-If a lifeguard is not available, have someone call 9-1-1.

-Throw the rip current victim something that floats--a lifejacket, a cooler, an inflatable ball.

-Yell instructions on how to escape.

-Remember, many people drown while trying to save someone else from a rip current.