Do you love to swim in the ocean? Who doesn't, right? The sand, the sun, the cool water…what's not to love? But have you ever been in the water and suddenly felt a sinking pull?

Uh oh! A sinking feeling is the last kind of feeling you want when you're in the water. But many people experience this feeling when they're at the beach. As they play in the water, they suddenly feel like they're being pulled toward the bottom and away from shore.

What's going on here? More than likely, they're experiencing a phenomenon known as a rip current or an undertow.

An undertow and a rip current are both caused by the action of waves breaking on the shore. An undertow is usually much milder than a rip current. However, undertows have been known to have enough power to sweep swimmers out to sea.

Why do these underwater currents occur? Think of what happens in an ocean. Waves continually break upon the shore. One after the other, they never stop. All that water has to go somewhere, right?

As waves break on the shore, water from previous waves runs underneath the waves currently breaking on the shore. This creates a gentle current that runs along the bottom of the ocean, which can pull you toward the ocean floor. This is an undertow, and it's usually mild enough that it doesn't present any danger except to small children and the weakest of swimmers.

Sometimes, though, certain weather patterns cause heavy wave action. At these times, the water from breaking waves may not be able to get out and it builds up. As it does so, it seeks a weak point in the breaking waves. When it finds one, it pushes quickly out to sea, creating a rip current that runs quickly away from shore along the surface of the water.

Rip currents can be very strong. So strong, in fact, that they can sweep even strong, experienced swimmers out to sea. Strong rip currents can even be deadly. As many as 150 people die each year in rip currents. For example, in Florida, rip currents cause more deaths every year than thunderstorms, hurricanes, and tornadoes combined!

Some areas are more prone to rip currents than others because of the particular shape of the coastline in the area. You may see warning signs in these areas telling swimmers to be wary of rip currents.

If you're WONDERing what to do if you ever find yourself caught in an undertow or a rip current, you might be surprised by the answer.

Unfortunately, the natural reaction to swim toward shore can be deadly in the case of a rip current. Even strong swimmers can tire out quickly before ever reaching the shoreline. Instead, the best thing to do when caught in an undertow or rip current is to swim sideways along the shoreline — parallel to shore — until you find a weak point in the current that will let you head back to shore safely.

If you're swimming in an unfamiliar area, be sure to ask locals about the currents in the area. You should also be aware of any posted warning signs and take them seriously. Ignoring them can be a costly, potentially deadly mistake!

Wonder What's Next?

The subjects of tomorrow’s Wonder of the Day may be different, but they can both make you very sick!