Red arrows point to rip currents on a crowded Delaware beach. Rip currents are not nearly as easy to spot from the beach as from the air. (Delaware Sea Grant)

“You have a better chance of winning the lottery than being killed by a shark,” says Stephen Leatherman, who’s known as “Dr Beach,” and the annual listing of the Top 10 Beaches he issues before each Memorial Day weekend.

Many beach goers fear sharks more than anything else, he says, but “only one person on average is killed annually in the United States by sharks, which pales in comparison to the 100 plus people who drown and tens of thousands of swimmers who struggle in deadly rip currents each year.”

Leatherman is a professor and director at the Laboratory for Coastal Research at Florida International University in Miami. From 1981 to 1997 he was a professor at the University of Maryland, College Park and taught a popular course on waves and beaches. He’s conducted scientific studies of rip currents.

A rip current is a stream of water flowing back into the ocean from near the shore. As waves wash ashore the water returns to the ocean as the “backwash,” which you can feel around your feet when you stand in the water.

This isn’t dangerous, but at times the water running back into the ocean becomes concentrated into rip currents.

1) Incoming waves create an underwater sandbar close to shore; 2) Sandbar blocks water from flowing back to ocean; 3) Part of the sandbar collapses, water rushes though, creating a rip current; 4) Once though the gap, the rip current weakens but can continue carrying a victim.

After the rip current reaches the area where waves are not breaking it weakens and dies. But, this is often too late for swimmers caught in one.

Even if you’re an Olympic swimmer caught in a rip current, you shouldn’t waste your energy swimming like mad toward the shore. An ordinary swimmer will soon tire fighting the current and is likely to panic.

Life guards offer this basic advice to those caught in a rip current: swim parallel to the shore, not toward it. Since rips are rarely more than a few feet wide you’ll escape and can then swim toward shore.

By the way, life guards at ocean beaches are rip current experts—pulling people out of them. Asking lifeguards about rips is a good idea.

Instead of trying to remain calm and remembering to swim parallel to the shore, you’re obviously better off not not getting caught in a rip current. If you’re with children you need to be especially watchful; many victims drown while trying to rescue a child or children from a rip.

Almost all beaches with lifeguards use a system of flags to warn bathers of dangers, including rip currents. When you arrive at the beach you should find out what the different color flags mean. Generally a red flag will mean you should stay out of the water because of rip currents, dangerously rough surf, or other hazards.

Finally, before leaving for the beach you can check National Weather Service surf forecasts of wave size, water temperatures, and the likelihood of rip currents.

These forecasts for the Mid Atlantic are on the Web:

Forecasts for Delaware and New Jersey Beaches

Forecasts for Maryland, Virginia, and North Carolina Beaches

Also, check out this National Weather Service rip current video.