A trip to the beach is the ultimate holiday escape.

Picture yourself basking in the sun with soft sand beneath your feet and the gentle ocean waves lapping against your legs.

While soaking up the beauty of the ocean, it’s important to stay safe in the water. Always be mindful of the waves and never turn your back on the sea.

You may be familiar with rip currents and shifting tides, but have you ever heard of square waves?

Yes, square waves really do occur, and while they may look beautiful, they can also be one of the most dangerous phenomena to encounter in the ocean.

A square wave, or “cross sea,” forms when two sets of waves collide, creating a square-like pattern that resembles a checkerboard. According to the European Space Agency in 2010, these conditions are relatively common in the ocean, especially when a windsea and a swell, or two separate swell systems, meet.

A 2004 study referenced by the agency revealed that "a significant number of ship accidents occur in crossing sea states."

As noted by HowStuffWorks, square waves are rare but tend to appear near the coast. A great place to observe them safely is along the western coast of France, particularly on Île de Ré.

Cross-seas can make navigation difficult for boats and swimmers. Waves can reach up to 10 feet, and the winds can change direction, making it more hazardous.

While this occurrence is unlikely, if square waves do appear, it’s wise to avoid swimming or going out on a boat, as conditions can be rough.

Instead, consider enjoying the sand or dipping your toes in the shallows until conditions improve. When the weather calms down, you’ll be able to safely return to the water without the crowds.

What should you do if you're caught in a square wave?

In the water, you might not immediately notice the grid-like pattern of the waves, but you’ll likely feel the increasing swells and the struggle to swim against two opposing currents.

The best strategy is to avoid venturing too far out into the water in the first place. If the waves get too large, it’s safest to exit the water as soon as possible.