A trip to the beach often feels like the perfect holiday escape. The sound of waves, the warmth of the sand, and the refreshing sea breeze can make for a day of relaxation and joy. But while the ocean is beautiful, it is also unpredictable. To enjoy it safely, beachgoers need to recognize and respect its hidden dangers.

Most people know to watch for rip currents, shifting tides, or strong surf conditions. Yet one of the most visually striking and lesser-known natural phenomena is the “square wave,” also called a cross sea. Though fascinating to look at, this rare sight can be extremely dangerous for swimmers and boaters alike.