You swim as hard as you can in the sea toward the shore, but you find yourself farther and farther away from the shore. Chances are, you are running into a hidden danger: a rip current.

A rip current is a strong flow of water running from a beach back to the open ocean, sea, or lake. Rip currents can be more than 45 meters wide, but most are less than 9 meters. 

Rip currents can move at 8 kilometers per hour, faster than any Olympic swimmer!

According to National Geographic, rip currents can form in a gap between sandbars, piers, or parts of a reef. Such underwater obstacles block waves from washing directly back to sea. The water from these waves runs along the shore until it finds an opening around the obstacle.

The stream of water, now a rip current, rushes to the opening and returns to the sea. 

A rip current flows more quickly than the water on either side of it, and may stir up sediment from the beach, which makes rip currents easy to spot as dark or muddy lines running from the beach out toward the ocean. Rip currents are also usually more calm-looking than the surrounding water. 

If you are caught in a rip current, what can you do to survive?

Never try to swim against a rip current! A rip current is a powerful opponent which can make you use up your energy. Instead, you should stay calm and relax in order not to let rip currents pull you under, and swim at an angle away from the current toward shore when free from the pull of the current.

About The Blue World series:

The ocean covers more than 70 percent of the Earth. In this blue world, there are all kinds of marine life with surprising abilities we don't know about. In this series, CGTN guides you through the journey of exploring the amazing animals in the ocean. 

For more:

The Blue World: The mystery of the sex of green turtles

The Blue World: Brainless jellyfish

The Blue World: Half asleep, half awake dolphins

The Blue World: Never make a pufferfish angry

The Blue World: From round fish to flatfish

The Blue World: When a whale sinks into the sea

The Blue World: Sea otter's treasure chest

The Blue World: Mother octopuses' mission

The Blue World: When the beauty of coral fades

The Blue World: Whale beachings

The Blue World: A shark's sixth sense

The Blue World: The glowing sea

(All images via VCG)

(If you want to contribute and have specific expertise, please contact us at nature@cgtn.com.)