Dangers of swimming in the North Sea

Noordzee, de gevaren van het zwemmen in zee. Strand zeehond

Dangers of swimming in the North Sea – The Dutch Coast

North Sea dangerous? North Sea most dangerous sea?
Every year, many people get into trouble in the North Sea. Especially the dangerous currents along the coast cause people to drown every year. With this knowledge you can safely enjoy the sea.

Summer has really started and many people are looking for a cool sea. Besides the local beach visitors, many people from other parts of the Netherlands come to the sea for a day, not to mention holidaymakers from home and abroad. It is striking that mainly people who did not grow up by the sea, are not aware of the dangers of the North Sea. It often happens that parents let their children play in the sea unsupervised. The dangers of the North Sea are often underestimated. Swimming in the North Sea is not comparable to swimming in a lake or river. When you take a dive in the North Sea, it is wise to know what the dangers are.

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Don’t go too deep into the North Sea

When you seek cooling in the sea, it is wise never to go too deep. If you do decide to go further into the sea, don’t go alone. Swimming in the North Sea can definitely not be compared to swimming in a clear sea, where it looks like lying in an aquarium.

Never let children play alone in the sea. Make sure there is always supervision. Children can easily be overthrown by waves and pulled along by the strong currents in the North Sea. This is because the North Sea has dangerous and strong currents that cause problems for many people every year. Besides the question whether children can swim well enough and long enough, hypothermia and panic can cause serious problems. The latter also applies to adults.

Currents at the Dutch Coast

The North Sea on the Dutch coast has treacherous currents. It can certainly happen that you are swimming, and without you noticing it the current takes you deeper into the sea. Many people who are taken by the current into the sea, try to swim back to the beach against the current. This is dangerous because swimming against the current takes a lot of energy, while you will probably still be dragged deeper into the North Sea by the current. In that case, exhaustion is often the cause of drowning.

Children playing in the waves can also be overthrown and dragged along by the current. The children then panic which results in dangerous situations. The North Sea is quite dangerous, especially close to the coast.

What do you do when you are pulled along by the current?

When you are pulled along by the current it is the best choice to just let yourself be carried further out into the sea. At some point the current will decrease after which you can swim left or right out of the current. That is the moment to swim diagonally back to the beach. Keep an eye on the current of the North Sea. If you notice that you are pulled back into the sea, let yourself be carried back into the sea and leave the current on the side when it decreases.


Currents are always present in the sea, but many of the stronger, unexpected currents are often caused by muien. These muien, among others, make the North Sea a dangerous sea.

The sea is not equally deep everywhere. There are sandbanks under water. Between these sandbanks there are deeper channels through which the water flows faster, especially at low tide. When the water flows back to the sea, the current in a mui is soon too strong to swim against it. As mentioned above, it is important that in that case you do not panic but let the current carry you along to the sea, until you can swim out of the current. Muien in the North Sea are dangerous because you are pulled straight to the sea by the current.


Many people are less familiar with zwinnen than muien. They look like muien, with the difference that they are parallel to the coast and that they are at right angles to the coast. When the water retreats, the water from the zwinnen flows back to the sea via the muien. So zwinnen can also be dangerous because they lead you to muien.
It may well be that you are pulled along by the current, but that you also float parallel to the coast and a little later straight into the sea.

Offshore wind and the upper current

When the wind blows from land into the sea, you speak of a ‘offshore wind’. The danger of a offshore wind is in the upper current of the seawater. For example, look at a lake when the wind is strong. You will then see waves on the lake that move with the wind. The same happens at sea. When there is a offshore wind the wind pulls the water on the surface towards the sea. The harder the wind blows, the harder the water is pulled along by the wind. The current created on the surface is called the upper current. The dangerous thing about a offshore wind is that you are pulled along by the current towards the sea, especially when you are lying on an air mattress or other floating object. A strong upper current in the North Sea is certainly dangerous. This comes on top of the danger of the muien, zwinnen, Zoper and undertow.

When you are pulled along by the upstream stream towards the sea, the same applies again as indicated above. When you notice that the upper current is too strong to swim against it, it is safest to let yourself be carried deeper into the sea. Swimming against a too strong upper current will cause you to become exhausted and you will get further into trouble. So let yourself be carried away to the sea and try to attract people’s attention. Do not panic. You can also look around you to try to discover a sandbank where you can swim to. Further on in this article you will read how to recognize shallow water in the sea by the waves.

Onshore wind and undercurrent

A offshore wind is therefore dangerous, but a onshore wind, in which the wind blows from the sea to the coast, is certainly no less dangerous. A strong onshore wind creates a strong undercurrent. So what is so dangerous about the North Sea with a onshore wind?

With a onshore wind, the North Sea water is pulled along at the surface towards the coast by the wind. You would say that this does not make the North Sea dangerous, because the upper current goes towards the coast, and thus takes you to the beach. It is true that the upstream goes towards the coast, but all that extra water that is blown hard to the coast in the upstream has to go back into the sea. All that water goes back into the sea via the bottom. This means that the North Sea water on the surface flows to the coast, and that the water underneath flows off the coast. Because a lot of extra water is brought to the beach, which also has to go back into the sea, you get a strong undercurrent off the coast.

The danger of an undercurrent is mainly for children and the elderly, but anyone can get into trouble because of it. The seawater pulls you upstream towards the coast, while at the same time the undertow pulls you down towards the sea. Especially in the surf you can easily be pulled over and go under.
It is therefore not wise to go deeper into the North Sea than your knees in a strong onshore wind.

Zoper [slanting wind from sea]

Of course, the wind does not always blow straight into the sea or straight to shore. The wind often comes from the sea diagonally towards the coast. So-called Zopers can also make the North Sea really dangerous. In a Zoper, the water flows parallel to the coastline. Swimming against the current is usually very heavy or impossible. This can reinforce the effect of the dangerous flow of the muien and zwinnen as described above. When you end up in a Zoper, let yourself be carried away by the sea until the current decreases. Try to swim diagonally back to the coast from there. Do not panic. When you don’t come back to the coast, try to attract people’s attention on a stretch where the current is less strong, or look for a shallow stretch in the sea (sandbank).


Airbeds, straps and other floating material is of course delicious to use in the sea, but it also brings with it an extra danger. You drift easily, especially when there is a offshore wind. It is hard work to get back to the coast on your own. There is also a chance that you will have to be taken back to the beach by the rescue team.

What do you do when you see that someone is in danger in the North Sea?

Imagine you’re sitting on the beach or you’re walking and you see someone in the North Sea who is in danger. Then don’t wait to see if that person is waving at an acquaintance or friend on the beach. If someone is really in danger, or if you immediately see that something is wrong, warn the rescue team immediately. If a post from the rescue team is not very close, don’t hesitate to call 112. State exactly where you stand. Usually there are poles on the beach that you can recognize, the number of the beach strike (passage from the dunes to the beach), or the name of the nearest beach club. Through the emergency center 112 the rescue team will be alerted. Stay where you saw the person who is in danger in the North Sea, in order to immediately send the emergency service in the right direction.

Many people who get into trouble are day trippers who don’t know how dangerous the North Sea is.

Beach flags for information

Along the entire Dutch coast where day trippers come to the beach, rescue brigade posts can be found. At these rescue brigade posts, beach flags indicate whether you can safely enter the sea, and what the dangers of the North Sea are at that time. The flags used are the same in all countries.

  • Orange windbag : You are allowed to go into the sea, but it is forbidden to use floating objects such as air mattresses, pneumatic tires etc. This because of the danger of drifting towards the sea for one of the reasons mentioned above.
  • Yellow flag : Swimming in the North Sea is not recommended because it is dangerous, but it is not yet forbidden. So be careful. Floating objects are forbidden in the sea.
  • Red flag : A red flag on the beach means that you are not allowed in the sea. It is too dangerous to swim!
  • Red-yellow flag : If you see a flag that is red at the top and yellow at the bottom, it means that you are on a beach where lifeguards are watching you. It is forbidden to do water sports here. Although you have to think of your own safety when you go into the North Sea, you will also be watched by the lifeguards, which makes you feel safe.
  • Black and white checkered flag : In the zone delimited by black and white checkered flags, you are allowed to practice water sports. Of course, this only applies to the water sports that are allowed. For swimmers it is a bit of a caution here, perhaps you should move to an area marked by red-yellow flags.

How to recognize shallow water from the shore

From the beach you can guess where the dangerous muien and zwinnen are in the North Sea.

When you stand on the beach you can recognize shallow water if you know what to pay attention to. From the beach you can already see where sandbanks are under water and where the water is shallow and where the seawater is deeper. From the beach you can already make a small estimation where the muien and zwinnen are.

Shallower stretches can be recognized by the turning of the waves, so the white heads of foam. Often you see waves turning on a certain part of the sea, this is the shallower part. This is where you should be able to stand.

When you follow waves from that point towards the coast, you will often see that the waves get higher but don’t turn, which indicates a deeper part in the sea. Recognizing shallow water can certainly be important if you swim in the sea and get into trouble. You can then try to swim to that shallower part so you can stand up.

Jellyfish in the North Sea

You will encounter jellyfish in every sea, including the North Sea. Day trippers who do not come from the coastal region often wonder whether there are dangerous jellyfish in the North Sea.

The North Sea is popular with jellyfish. This is due to the favourable living environment for the jellyfish. There are days when the presence of jellyfish in the seawater can ruin your day at the beach. Especially with a offshore wind, so when the wind blows from land into the sea, the chance of jellyfish is higher. When the wind comes from land, the undercurrent in the sea towards the shore will become stronger, and jellyfish can take to the shore.

Do you have to worry about jellyfish in the North Sea?
Are there dangerous jellyfish living in the North Sea? In principle, the jellyfish in the North Sea are not dangerous. They can be very annoying. When you are stung by a jellyfish (also known as a jellyfish bite), it can cause a lot of itching and pain.

What to do when you are stung by a jellyfish
You’re nice in the sea, and suddenly you feel an annoying feeling….. you’ve come into contact with the poisonous tentacles of a jellyfish. As long as you’re not allergic to jellyfish bites, you don’t have to worry. It is only annoying then. If you are allergic, a jellyfish bite can be dangerous.

Treatment jellyfish bite

Treatment jellyfish bite:

  • Rinse the spot where you were stabbed well with seawater. Do NOT use fresh water.
  • Do not scratch or rub, this will make the problem worse.
  • See if there are any tentacle remains attached to the skin. Carefully remove them with gloves or tweezers.
  • Against the itching you can use the same remedy as you use against the itching of insect bites.
  • If you get headaches, respiratory problems, shortness of breath or vomiting, this may indicate an allergic reaction. In that case it is important to seek medical help immediately.

Lesser weever – poisonous fish North Sea

It is not common knowledge, but also in the North Sea lives a poisonous fish, the ‘lesser weever’. The lesser weever normally lives in the Eastern Atlantic Ocean and the Mediterranean. This very poisonous fish also occurs naturally in the North Sea. Due to the warming of the seawater, the poisonous weever is becoming more common on the Dutch and Belgian coasts in the North Sea.

The lesser weever lives close to the beach in shallow water and on sandbanks, so exactly where people walk in the sea. Here the fish digs in, in the sand. If you accidentally stand on the weever, he will use the poisonous spines on his dorsal fin to defend himself. Not a nice idea, especially if you know that the weever is one of the most poisonous fish in Europe.

Treatment stitch of the lesser weever

The lesser weever is actually the most dangerous fish in the North Sea, at least near the Dutch and Belgian sea coast. What do you do when you are stung by a poisonous lesser weever.

When you have been stung by this poisonous fish, you can expect severe and burning pain. A sting by the lesser weever is in principle not lethal but mostly very painful. Always see a doctor in case you have an allergic reaction.
If you don’t treat the sting, the pain can spread and last for weeks.

The poison of the lesser weever is thermolabile. This means that it breaks down quickly when exposed to higher temperatures. The best treatment is to heat the spot where you were stabbed as quickly as possible to a temperature above 40 degrees Celsius, and keep doing this for at least 15 minutes.

Enjoy the sea but make sure you are familiar with the dangers of the sea. Never let children play alone in the sea. The North Sea has dangerous currents that can really get you into trouble, but is the North Sea the most dangerous sea? Every sea has its own dangers, at the North Sea it is the dangerous currents. The North Sea is certainly not the most dangerous sea if you know what you are doing.