On August 17, 2003, waves rolling down the 400-mile-long open stretch of Lake Superior were crashing onto the sand beach at Park Point in Duluth, Minnesota. The water piling up along the sand escaped via a “rip current,” an alley of high-velocity water cutting through the waves, back into the lake.

Junior Lessard, then a University of Minnesota athlete, was swimming in the pounding surf when he found himself swept away from shore.

“I was swimming my hardest, trying to get back to shore and not going anywhere,” Lessard said, according to the Sea Grant Minnesota institute. “I felt hopeless. It was like slow motion.” The exhausted Lessard was spotted and rescued about 10 minutes later, towed to shore and rushed to the hospital.

Lessard, who would go on to play professional hockey, was one of six lucky swimmers rescued that day. Another swimmer died in the current.

Related: A Day at the Lake? Save Yourself a Mountain of Trouble

What is a rip current?

Most often associated with oceans, rip currents can also form on big lakes. No matter where they appear, they’re dangerous, accounting for as many as three-quarters of surf zone fatalities.

Rip currents are not the same as “undertow,” the thin layer of water that runs out to sea along the sandy bottom between each breaker and can sweep people off their feet but not carry them any appreciable distance.

Rip currents are usually 20 to 100 feet wide. They can run as fast as 5 miles an hour — faster than any human can swim. Rip currents will not pull you under, but they can sweep you hundreds of yards from shore, with a velocity up to 8 feet per second.

Where does a rip current come from? Onshore winds from the northeast to east have a lot to do with it. They create big waves, which crash onto a beach or plow into an obstruction like a pier or jetty. All that water piling up near the shore has to go somewhere, so it finds a way to escape to the sea, perhaps by carving a break in a sandbar. The result is a rip current.

The bigger the waves, the stronger the current and the greater the danger.

More than 100 people die in the United States each year as they are carried away from shore by rip currents, according to the United States Lifesaving Association.

Rip current on Grant Ave Beach“They’re only dangerous if you don’t understand them

The trouble begins when people follow their natural instincts.

“If you’re in a rip current, getting pulled away from shore, your instinct is to swim back to shore,” says Dave Benjamin, executive director of the Great Lakes Surf Rescue Project. But, says Benjamin,“These dangerous currents are faster and stronger than Olympic swimmers.” If you’re fighting the currents, he says, “you normally don’t have a chance against them.”

“They’re only dangerous if you don’t understand them,” says Benjamin. “You want to think of them as a treadmill. If you’re running on a treadmill, no matter how fast you run, you’re not getting anywhere. The only way to beat it is to get off of it.” (Photo: Chris Brewster, USLA/NOAA)

How to survive a rip current

“What we advocate is that people flip, float and follow the safest path out of the water,” says Benjamin. This means following these steps:

1. Swim parallel to shore. Turn and swim sideways (that is, parallel to the shore) until you escape the fast-running water. Rip currents are usually narrow and often less than 100 feet wide. If you’re having trouble at any point, lift an arm and wave for help.

2. When you’re out of the rip current, swim at an angle away from the current and toward shore.

3. If you’re out of energy at any point, stay calm and float. If you find yourself tiring, the most important thing to remember is to flip over and float.

One North Carolina woman told the National Weather Service that after being pulled out to sea by a riptide, she swam parallel to shore but the current was so strong that she began to flag. “Then a wave broke over my head, and I felt the panic rising,” she said. “I know that panic is one's worst enemy in the water, so I floated and treaded water for a few minutes to catch my breath and relax.” (It was then that she noticed some surfers even further out and swam to them for help.)

If you’re on shore and see someone caught in a riptide, call the lifeguard or 911. Push him something that floats, such as a boogie board or cooler. Yell for him to swim parallel to shore till he escapes the pull of the current. (Photo: NOAA/NOAA)

Related: Silent Drowning: How to Spot the Signs and Save a Life

How to avoid a rip current

north carolina rip currentOf course, the best way to avoid getting caught in a rip current is to not go near one. Some rip currents are obvious, even to the untrained eye. The outgoing current, cutting against the incoming waves, often looks like a path or river. It disturbs the pattern of the surf and is often colored with sediment, foam and debris.

But some rip currents aren’t obvious. Lifeguards know and will tell you what areas to avoid.

Before you go to the beach, check the National Weather Service (NWS) surf forecast. Some areas broadcast the threat of rip currents daily, classifying them as low, medium or high risk. Children will be safer in life jackets even when the risk is low.

The NWS and its parent agency, the National Oceanic and Atmospheric Administration (NOAA), run a riptide safety campaign. NOAA and the National Weather Service also suggest learning how to swim in surf, checking beach warning signs, avoiding solo swims and staying within clear sight of the lifeguard stand.

Even on calm, sunny days, their experts warn, life-threatening rip currents can still develop.

If you are caught in one, the most important thing is to stay calm and focused. “Calm yourself down, get your breathing under control,” says Benjamin. “You may have to float until rescue.”

“Focusing on floating is what can save your life.” (Photo: Jeff Otto, Wilmington Star News/NOAA)

Related: How — And When — To Perform CPR

Greg Breining is a Minnesota-based journalist who writes about science, travel and nature for national and regional magazines, including Audubon and National Geographic Traveler. His books about the natural world include Wild Shore and Paddle North.