If you see square waves forming a chessboard grid on the sea surface, you need to get out of the water immediately, according to safety experts. These so-called cross waves can reach up to 10 feet tall and have been linked to numerous shipping accidents.
Oceanographers explain that square waves are created when weather patterns force water to form waves from different angles, resulting in a dangerous cross sea. The European Space Agency (ESA) records indicate that a large portion of shipping accidents between 1995 and 1999 occurred in such conditions.
Mathew Giachetti of the United States Lifesaving Association (USLA) advises: 'If caught in a square wave, the most important thing to do is get out of the water immediately. Stay calm, try to float on your back, and swim parallel to the shore to escape the wave's force.' He adds that swimmers should carefully make their way back to land and signal for help if necessary.
Cross waves have recently been observed on the Aegean Sea off Turkey, as well as in the South Pacific, Atlantic Oceans, and off the island of Île de Ré near La Rochelle, France. The Phare des Baleines lighthouse on Île de Ré offers a popular vantage point for viewing the phenomenon—but authorities urge visitors to stay out of the water.
