The wave motion of the sea is a complicated phenomenon and subject to numerous variables. One of the most fascinating (and rare) is without a doubt what creates the square waves, which usually generates a checkerboard-like pattern on the surface of the water. Despite appearances, however, it is not recommended to go into the sea when these waves are encountered.
Also called cross seaThese are formed when waves moving in alternate directions meet at right angles. They occur when bad weather (such as tropical storms) pushes waves in one direction while current moves in another, somewhat like rivers reversing.
It is usually not recommended to go to sea when you notice this phenomenon, both for simple bathers and especially for ships. However, in shallow water where currents are not strong and are mitigated by the coast, square waves they do not normally pose a danger to swimmers and confident surfers (like the one who rode the biggest wave of all).
Where square waves get really dangerous is obviously offshore, where currents and opposing wave water volumes can build up and cause ships to roll severely. This puts boats and vessels at risk of taking on water and can exponentially increase the likelihood of an accident.
Research, think, has discovered that a large number of accidents have occurred precisely because of this phenomenon… other than the Bermuda triangle!