What causes terrifying ‘square waves’ that mean you should get out of the sea instantly

If you see square waves in the sea that form a chessboard grid, you need to get out of the water immediately. Here's why.

Some strange things can happen in the water when the weather gets wild or as a result of currents.

These include a terrifying fog ‘tsunami’ that really does look like the real thing; bizarre waterspouts that form on lakes, rivers, and at sea, and powerful whirlpools that can drag objects into its surface, according to the National Ocean Service (NOAA).

Another scary occurrence that can take place in the ocean is the formation of square waves.

Like you would expect, these basically look like a chessboard on the surface of the water - but they’re anything but fun and games.

In fact, they’re actually insanely deadly, according to the European Space Agency (ESA), whose records claim a large portion of shipping accidents occurred in cross seas between 1995 and 1999.

Square waves can be very dangerous (Razvan Fiat)

These grid waves can reach up to 10 feet tall and can cause ships to experience navigational problems.

Oceanographers believe that these square waves - also known as cross waves - are made by weather patterns forcing the water to form a wave from different angles.

While they do make for a remarkable sight, this checkerboard pattern can spell disaster for swimmers, surfers and even boats.

Surfer Today says that the waves are also often associated with strong and localised rip tides.

So if you are doing some backstroke and suddenly find yourself swimming amongst squares, it’s recommended you get out of the water ASAP because they pose a serious threat.

Mathew Giachetti, of the United States Lifesaving Association (USLA), previously told Islands.com: "If caught in a square wave, the most important thing to do is get out of the water immediately, as they are extremely dangerous.

If you're caught swimming in square waves, stay calm and try and float on your back (YouTube/Razvan Fiat)

"Stay calm, try to float on your back, and swim parallel to the shore to escape the wave's force. Then carefully make your way back to land as soon as possible; if you can't reach the shore quickly, signal for help."

Cross waves were recently seen on the Aegean Sea, off the coast of Turkey. They have also been spotted in the South Pacific and the Atlantic Oceans, as well as off the island of Île de Ré.

The coastal spot, situated near La Rochelle, is 30km wide, and is a popular spot for tourists wanting to catch the quadrangular waves in action.

Many people head to the Phare des Baleines (Whale Lighthouse) on the island for the best view—just stay out of the water, please?