What Are Square Waves — And Why You Should Avoid Them

Last Updated March 24, 2023

The world can be a dangerous place — what may seem like a beautiful and harmless phenomenon could turn out to be a deadly encounter if you’re not careful enough. In the west coast of France, you’ll find Phare des Baleines (Baleines Lighthouse), a famous spot in Île de Ré where tourists come to watch square waves or the grids in the ocean surface known for destroying ships and drowning people who get caught inside of them. 

So what exactly are these square waves and how perilous are they? In this article, we’ll be talking about their risks and how you can keep yourself safe if ever you encounter them.

What are square waves?

As if there aren’t enough things yet to get scared about the ocean like the Great Whites and whirlpools, there’s a new kind of fear you can add to the list of what you should avoid in the water — square waves.

Also referred to as cross-sea, these waves occur when two different swells from opposing directions meet. You see, waves normally travel in parallel and break horizontally in shores, but in rare occasions that a cross-sea happens, the waves collide in right angles instead, forming the unique block pattern that can be seen above the water surface. 

Square waves occur because of varying conditions. For instance, it can happen in places near the coastline where there are two seas or two weather systems that come together in certain periods. Since the seawater from the different conditions intersect but do not mix, cross-seas happen. You’ll see how these grid waves look like in the 0:15 to 0:20 mark of the video below.


Ships and small boats in the ocean are at more risk in the event of occurring rogue and square waves. In fact, most accidents happen when there’s a crossing sea or when the wind and sea are almost aligned.

According to research, colliding two-dimensional waves can cause the formation of wave packets that are three times more coherent than the amplitude of initial waves. When this happens, freak waves form peaks that can reach up to 10 feet  — a dangerous hazard that’s already caused multiple shipwrecks and boat capsizing all over the globe. 

What about for humans? Although this rare phenomenon looks beautiful when seen from above, the danger it poses is located under the water surface. In an unfortunate event that you get caught in the middle of a square wave, the riptides will pull you out of the ocean, drag you under the water, and have the currents play ragdoll with you.

If you’re lucky, you might get out unscathed. If not, the fatigue of trying to fight off and get out of two different currents will cause you to drown or die. 

But as scary as it seems, you should know that this anomaly doesn’t last for long. When local winds interfere with these waves, they lose energy as they travel and dissipate just within minutes after they started. When the square waves pattern starts to fade, that’s when you know it’s safe to get back to the sea.

Places Where there are Crossing Seas

Crossing seas or square waves are the kinds of waves that you don’t want to encounter whenever you’re swimming or surfing. But surprising at it seems, there are still several people who travel to witness this rare occurrence.

Since these specific waves are the result of wave refraction and diffractions, they’re mostly seen in coastal regions or inside tiny bays. The most well-known place you can watch these waves is in Île de Ré.; however, you can’t expect to see the square waves a hundred percent of the time. If you want to check them out, you need to check the local reports every day. 

There are news and articles that claim this small island in France is the only place where cross seas happen, however, this is entirely false. You can also see these square waves in Tel Aviv and in Lisbon, Portugal. In these locations, tourists often fly a drone over the sea or get up a lighthouse to get a bird’s eye view of the waves. 

Hey, there’s also a chance that you’ve already encountered square waves near the shore, but you just didn’t know it. Shallow square waves are safer because they have less powerful currents, like the ones in the video below for example.

Surfing in Square Waves

So if crossing seas in the ocean consist of strong currents and waves, is it possible to surf right through them? 

Okay, calm down, Evel Knievel. Before we continue this discussion further, may we remind you again of how risky it is if you ever get caught up in square waves. Now, in regards to that question — Yes, it’s totally possible to surf square waves (but we highly discourage it). As it happens, there isn’t enough evidence to support that square waves in shallow areas are dangerous for swimmers and surfers. 

The mainstream media portrays square waves to be highly dangerous and deadly (which is also 100% true); however less than powerful interacting swells are surf-able. According to some, the experience of surfing a square wave is kind of similar to riding a wedging wave. 

If you’re a pro or advanced rider who’s looking for a new experience or a cool story to impress your peers, then we suggest you think twice before going in. But if you’re a beginner surfer, don’t even think about doing it.

Got caught in a square wave?

Here’s some bad news — not-so-good swimmers are more likely to drown if they get caught inside square waves. But the good news is, floaters and level-headed people have more chances of surviving it. 

In a viral photo uploaded on Twitter, a man was photographed swimming inside a square wave, oblivious of the impending danger he’s in. According to the post, the lucky guy managed to survive. So how did he do it? 

If you ever find yourself in the same situation as that guy in the photo, the best thing you can do is to stay calm and keep yourself afloat as much as you can. Getting caught in crossing seas is somewhat similar to being caught in a rip current, the only difference is that in a square wave, two currents are pulling you in every direction at the same time. 

Instead of fighting these currents, you must save your energy by keeping your head above the water. Avoid panicking, as it will only cause you to flap and paddle without direction, which will just waste precious energy. Since square waves only last a few minutes, it’s best you just wait for them to dissipate and swim to shore as soon as the current has weakened. 

Now, in an event that there’s someone else that’s caught in the middle of crossing seas, don’t attempt to rescue him/her. You’d only be putting yourself in danger as well. What you can do instead is call the lifeguard or the emergency phone number in your area and ask for help. You can also shout at them to stay calm and keep their head above the water until the waves have weakened.

How to Avoid Them

Square waves can be unpredictable and dangerous, so if there are reports and forecasts of these occurring, it’s best you steer clear out of the water. Remember, the best way to survive getting caught in a square wave is to avoid being in one.

Even though square waves are pretty uncommon and can only be found in certain locations in the world, it’s still important you know how to spot them. To do this, you need to get into a more elevated area to get a better view as square waves are easier to see from above. If you see chessboard-looking patterns forming in the surface of the water, alert the others. 

Changes in the current can also happen when you’re already in the water. If you, the lifeguard, or other people at the beach notices a slight change in the water’s movement and flow, get out of the water immediately. 

Some beaches are also known to have unpredictable waves and wind conditions like gale warnings, so there are flags located at the entrance or near the lifeguard indicating the forecasts for the day. If you’re new to a certain location, it’s useful to know what those flags indicate. Take a look at the photo below for reference. 

What is a Gale Warning

Frequently Asked Questions

Q: Are square waves dangerous?

Square waves are the result of the intersection of two swells coming from different directions, creating square-patterned riptides on the water surface. If this occurrence happens in deeper parts of the ocean, square waves can be dangerous not only for humans but boats and ships as well. 

According to research and statistics, one of the main causes of shipwrecks and boat capsizing are the currents brought about by crossing seas. For humans, however, getting caught inside a square wave is similar to being pulled in every direction by two powerful currents. 

Q: Can you surf in square waves?

Technically, yes. Professional and advanced surfers who’ve tried surfing in cross seas compared the experience to surfing a wedging wave; however, we do not advise doing so. Square waves in shallow shores are harmless but it’s still best to stay out of the water when grid-pattern waves start to appear on the deeper part of the ocean’s surface. 

Q: Where can you find square waves?

Cross seas or square waves are a rare phenomenon that only happens in certain locations such as the Island of Rhe in France, Tel Aviv in Israel, and Lisbon, Portugal. When square waves start to appear in the water, they don’t usually last long as they dissipate when the waves and wind have already weakened. 

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