Square waves aren't an oddity. Happens all the time when a storm front is incoming. Living on the Atlantic Ocean, I see it all the time; more so in the winter months.

"Square waves do not result from any circumstance that is taking place below the water. Instead, they're the result of the way the water is moving.

In other words, square waves result from the intersection of two seas, also known as cross-sea or grid waves.

A weather pattern in the region causes the waves to form at different angles. When two opposing swells collide, a unique pattern emerges."