IF YOU'RE SWIMMING TOWARD SHORE and the shore is moving away from you, you're probably caught in a rip current. You do have options — to swim out of the current or float with it — and both can work for you, but how well they'll work depends on what kind of swimmer you are and what kind of current you're in.

Rip currents are the offspring of incoming waves and the sandbars underneath them. When waves break over a sandbar, the backwash can be trapped in a trough, where it slides like a snake along the shore, looking for a break in the sandbars. When it finds one, it strikes straight out to sea, often with considerable speed, sometimes carrying swimmers and waders with it. According to a recent survey, rip currents on average kill more people per year than floods, tornadoes, lightning, or hurricanes. Sharks are more of a threat on television than on the beach where they average less than one kill per year.

Rips are more common when the waves are coming straight at the shore and sandbars are high enough to keep the backwash (sometimes called the undertow) from sliding straight back out under the incoming waves. They are more common during an ebbing tide when the trough water drops even further below the bars. During the slack of low tide, they may disappear altogether, leaving the sandbars, troughs, and channels exposed on the flats like a roadmap for tomorrow's rip current routes.

Not all wave trains come straight in. Many arrive at an angle to the beach, sometimes after traveling thousands of miles, and the result is a longshore current that flows down alongside the beach. Waves out of the northeast, for example, could set up currents flowing to the south. If you find yourself drifting well downshore from your beach blanket, you're probably caught in a longshore current.

As they cruise down the beach, these longshore flows can encounter nearshore sandbars and throw off eddies, small rips shooting off at odd angles. They can also throw off eddies if they bump into weak wave trains arriving out of the southeast. When a longshore current meets a jetty or a groin or a pier, it will swerve dramatically, creating a dangerous rip headed straight out to sea. Lifeguards call these "permanent rips," and they can be killers.

Bilingual Rip Current Signs To alert as many swimmers as possible about rip currents, Maryland Sea Grant has provided Ocean City with metal warning signs. Two years ago, the program presented 115 of these outdoor signs to the city and also sent 15 signs to the seashore at Assateague State Park. This summer, Maryland Sea Grant gave Ocean City 45 bilingual signs that carry warnings in both English and Spanish. The outdoor signs form part of an ongoing nationwide campaign by the Sea Grant network, the National Oceanic and Atmospheric Administration, the U.S. Lifesaving Association, and others to educate swimmers about the deadly dangers of rip currents­. In Maryland, the Sea Grant effort began with calls from U.S. Lifesaving Association Member Tom Lott and from Chad Whitehead, a former Ocean City lifeguard who’d witnessed firsthand how rip currents can drag swimmers into danger. To learn more, visit the web at: http://www.ripcurrents.noaa.gov/

As they cruise down the beach, these longshore flows can encounter nearshore sandbars and throw off eddies, small rips shooting off at odd angles. They can also throw off eddies if they bump into weak wave trains arriving out of the southeast. When a longshore current meets a jetty or a groin or a pier, it will swerve dramatically, creating a dangerous rip headed straight out to sea. Lifeguards call these "permanent rips," and they can be killers.

If you're caught in a rip, you have two options:

Plan A: Swim. Head for the side of the channel, swimming parallel to the beach or at an angle towards the beach. This is the most widely recommended advice. Swimming straight back against the current — with exhaustion as the likely outcome — is not a workable option.

Plan B: Float. Float and wait calmly for help. Eventually, somewhere beyond the breakers, the rips will slow down, spread out, and dissipate in the face of incoming sea swells, leaving you floating, perhaps not so far out from the beach. Some rips have been shown to curve back towards the beach.

Swim or float, which is your best option? To answer that you need to know yourself and you need to know your beach. Are you a strong swimmer with stamina? Can you float easily or tread water well (a trick that depends on body type as well as technique)? Are there lifeguards back there on the beach? If they're up there in the chairs, you can try floating and waiting for help. If the lifeguards are gone, and there's no one else around, you may need to swim. With both choices, calmness is key. Panic can be deadly.