If You Ever See Square Waves in the Ocean, Here’s What You Should Do Immediately

Summer is a time many of us enjoy by the sea—wading in the water, soaking up the sun, and embracing the carefree atmosphere. Naturally, this makes beaches especially crowded during the warmer months. However, even when surrounded by water and fun, it’s essential to stay alert. A single moment of carelessness can lead to serious danger. While many are familiar with the risks of shifting tides and rip currents, few are aware of the threat posed by square waves.

Visually captivating yet extremely hazardous, square waves—also known as a cross sea—form when two or more wave systems intersect at opposing angles, creating a checkerboard-like pattern on the water’s surface. According to the European Space Agency (ESA), these conditions arise when two swell systems, or a wind-driven sea and a swell, exist simultaneously. A 2004 study also noted that a significant number of maritime accidents have occurred under these crossing sea conditions.

Cross seas can generate swells reaching up to 10 feet tall, creating unusual wind patterns that make navigation challenging for boaters and swimming dangerous for anyone in the water. Although encountering these conditions is uncommon, if you do come across them, it’s best to avoid taking a boat out or swimming in such hazardous waters. Instead, it’s safer to stay on the shore, relax on the sand, and wait for calmer seas before venturing back into the water.

The Beauty and Danger of Square Waves

Square waves typically form in a few specific locations, often near peninsulas where two oceans or large bodies of water converge. The swells approach from different directions and sometimes bend around the peninsula, creating the distinctive square wave pattern. Notable spots to witness this phenomenon include the Isle of Ré, located just off the coast of La Rochelle in France, which is famous for its crossed sea waves. Another prime location is Cape Reinga in New Zealand, situated at the country’s northernmost point where the Tasman Sea meets the Pacific Ocean.

Square waves are visually captivating, which explains why locations like the Isle of Ré attract thousands of tourists eager to see the island’s lighthouse and the mesmerizing wave patterns. However, it’s important to admire these waves from a safe distance. Although it might seem unusual that intersecting waves at different angles draw so much attention, many people have never witnessed square waves in person. Interestingly, opposing swells can sometimes be seen in shallower waters, such as near the Isle of Ré and off the coast of Tel Aviv, Israel.

Scientists believe that square waves are a real-world example of the Kadomtsev-Petviashvili equation in action—a mathematical model that describes nonlinear wave behavior and helps explain how different weather systems interact.