Nature has a way of stunning us, and one of its rarest wonders is the phenomenon known as cross seas or square waves. These striking checkerboard-like patterns appear when two wave systems collide at angles over 45 degrees—often caused by wind pushing waves one way while ocean swells move another.
As mesmerizing as they look, cross seas are dangerous. The powerful, conflicting currents can trap swimmers, capsize boats, and even contribute to shipwrecks. A 2004 study found that many maritime accidents occurred under these conditions.
One of the best places to see them safely is from the lighthouse at Isle de Ré on France’s western coast, where the water grids often form. Waves can reach 10 feet high, making the waters nearly impossible to navigate.
So while cross seas are a breathtaking reminder of nature’s power, they’re best admired from a distance.
