One of nature’s wonders, which we are mesmerized by, is the unusual phenomena known as cross seas or square waves that form watery grids.

These grids are created when two sets of wave systems blend at different angles greater than 45 degrees, or when the wind pushes waves in one direction and a swell pushes them in another. However, no matter how beautiful these square waves look to the eye, they can be very dangerous for swimmers and ships.

What lurks beneath the breathtaking sight are currents that can wreck ships and pose a threat to people in the water because the water where these chessboard-like patterns occur is extremely difficult to navigate. Scientists believe cross seas is the reason for many boating accidents and shipwrecks.

In 2010, the European Space Agency said, “The conditions are quite common in the ocean and occur when a windsea and a swell, or two swell systems, coexist.”

It pointed to a 2004 study that showed “a large percentage of ship accidents occurred in crossing sea states.”

Along the western coast of France, at the Isle Rhe, this phenomenon is very common. However, as it is extremely dangerous to enter the water when it occurs, tourist get to witness the water grids from a lighthouse on the western part of the island.

Boats and swimmers can struggle to navigate these cross-seas since they can create waves as tall as 10 feet and alter wind patterns. Although this rarely occurs, if it does, avoid boating or swimming because the water conditions could be dangerous.

To learn more of this nature’s incredible phenomenon go to the video below.