A fishing crew was stunned when it found itself surrounded by a dangerous square wave phenomenon.
A video shows concerned fishermen scanning the sea as waves form a chessboard-like pattern.
The strange event was filmed in the Aegean Sea off the coast of Turkey.
Square waves, also known as a cross sea, are caused by two wave systems travelling at different speeds and trajectories.
The wave systems meet on the surface and resemble a grid or checkerboard.
Experienced surfers and boaters know to get out of the water when they see the rare wave pattern.
Square waves have reportedly caused many shipwrecks and pose a threat to anyone swimming in the water at the time.
The different swells from opposing directions can make it feel like you are battling against two competing currents.
Swimmers are at risk of being swept away while boaters can experience navigational problems.
A cross sea can sometimes be accompanied by waves of up to 10 feet, and unusual wind patterns, as reported by What’s The Jam.
Boaters are advised to stay in the shallows if they encounter square waves at sea.
