The next time you see latticed waves in the sea at the beach, get out of the water immediately.
Called the Cross Sea, they are so dangerous that they have even caused shipwrecks over the years.
Also known as square wavesthey can look interesting and are usually found in bodies of water, although they can be spotted closer to shore.
Places where they have been sighted are Francealso on the Île Re nearby Rochelle as well as near Lisbon in .
Cross seas are caused by two separate weather systems colliding.
They are very similar in rip tides which are difficult to get out of due to the two different wave directions.
To recognize them, they appear at the top of the water by a checkerboard effect on the surface.
They have even caused a number of shipwrecks over the years, according to the European Space Agency, as the ships were set in motion by the different directions of the waves.
A German research icebreaker named FS Polarstern reported a dangerously serious rolling incident allegedly caused by a cross sea.
If you want to see the cross waves, it’s best to see them from land to see the full effect while staying safe.
People on social media shared their experiences with square waves – and how dangerous they are.
One person on YouTube said, “Growing up in Hawaii, we were always taught to look for the ‘squares.’
“The grid can pull you back hundreds of yards and make it difficult to stay still.”
Waves around the world are getting stronger thanks to climate change, a report warns.
We’ve rounded up where to catch some of the world’s biggest waves.
A safer way to catch waves is in an inland surf lagoon – with the world’s first artificial inland lagoon found on the outskirts of Snowdonia
Or you can head to Bristol to try The Wave, a 180m high surf lake.