The United States Lifesaving Association estimates that 80 percent of rescues performed by U.S. lifeguards are caused by rip currents that suck water away from the beach.

So how do you spot them, and what should you do if you're caught in one?

The water that hits the beach when waves break needs to flow back to the sea, and it tends to do so in channels that form either along natural or man-made structures (such as cliffs or piers) or between waves. It's not always possible to identify a rip current, but according to the USLA they often appear as:

--"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"

Rip currents may appear to be calm patches of water, a phenomenon that sometimes proves alluring to unsuspecting swimmers. Surfers often use the currents to get beyond the surf break to await the next wave.

A helpful resource for learning how to identify rip currents is provided by Australian scientist Rob Brander, aka "Dr. Rip." His "Rip of the Month" page (www.scienceofthesurf.com/ripom.html) features various photos of rip currents. Explore his website for videos and other sources of information. For more information you can also visit www.ripcurrents.noaa.gov/overview.shtml.


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Getting out of a rip current

Experts say the important thing is not to panic. Do not fight the current by trying to swim directly back to shore. Instead:

--Try to swim parallel to the shoreline. Once you've gotten out of the current, head back to the beach at an angle.

-- Face the beach and signal or yell for help

-- If you cannot swim out of the current right away, be patient and tread water

Contact Aaron Kinney at 650-348-4357. Follow him at Twitter.com/kinneytimes.