Nature never ceases to amaze us with its beauty and unpredictability. Among its countless wonders, one phenomenon stands out for being both breathtaking and dangerous — the striking square waves, also called cross seas. These mesmerizing, grid-like patterns appear when two wave systems meet at an angle greater than 45 degrees, or when strong winds push waves in one direction while underlying swells force them in another. The result is a rare ocean spectacle that seems almost too perfect to be real.

While their geometric precision may captivate photographers and beachgoers, the truth is far more dangerous. Beneath the surface, powerful and unpredictable currents swirl, making these areas extremely hazardous for swimmers, surfers, and even large vessels. The turbulent water is nearly impossible to navigate, and in extreme cases, waves can reach heights of up to 10 feet. Ships caught in cross seas may find themselves struggling to stay afloat, and small boats are at even greater risk.

The European Space Agency warned in 2010 that “the conditions are quite common in the ocean and occur when a windsea and a swell, or two swell systems, coexist.” They cited a 2004 study revealing that a significant percentage of ship accidents happened in crossing sea states.

One famous location where this phenomenon occurs frequently is the Isle of Ré off the western coast of France. Here, tourists are advised never to enter the water when square waves form. Instead, they admire the sight from the safety of a lighthouse vantage point, where the symmetrical ocean grid unfolds without the risk.

Scientists believe that many historical shipwrecks may have been caused by cross seas. The pattern’s beauty belies its true nature — a chaotic battle of forces beneath the surface. If you ever spot these perfect squares forming in the ocean, it’s not the time for a swim or a photo shoot. It’s time to get out of the water — immediately.