Square waves, sometimes called “cross seas,” can create an unusual grid-like pattern on the ocean when two different wave systems meet at an angle. The result may look fascinating from above, but beneath the surface, the water can become highly unpredictable and dangerous.

These crossing waves can create unstable conditions for boats and powerful currents moving in different directions. Swimmers and divers may have difficulty staying in control, even when the water near the shore appears relatively calm. The unusual pattern on the surface does not show how strong or complicated the water conditions may be underneath.

Because of this, seeing square waves should be treated as a warning rather than an invitation to enter the water. The ocean can behave very differently from what a photograph suggests, and the conflicting wave patterns may make swimming especially risky.

If you ever notice this rare phenomenon, the safest choice is to remain on shore and observe it from a distance. Follow any warnings from local authorities and avoid entering the water until conditions are considered safe. As impressive as square waves may look, their beauty is best appreciated without getting too close.