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Toxic pietermannen surge at north sea beaches in Europe
Published on 04 Jul ‘25
Toxic Pietermannen Surge: Stay Safe on North Sea Beaches
Toxic pietermannen surge on North Sea beaches

If you’re heading to the beach this summer, watch your step. Marine experts from Vlaams Instituut voor de Zee (VLIZ) (Flanders Marine Institute) are reporting up to seven times more toxic pietermannen – weeverfish – than in previous years along the North Sea coastlines.

In Belgium, their presence has increased dramatically, especially along the sandy coastline. The Netherlands is also experiencing a rise in these venomous fish, with popular beaches such as Noordwijk, Texel and the Waddenzee reporting more frequent encounters and painful stings. In France, particularly along the Atlantic coast during the warmer months. These fish, known locally as “petite vive”, pose a seasonal risk. The United Kingdom is no exception. It is widespread, particularly in the south and west, and is responsible for numerous stings each year. Rising sea temperatures across the North Sea have created ideal conditions for this species to thrive, with more appearing near beaches in Germany and Denmark as well.

What are kleine pietermannen?

In Dutch, the term kleine pieterman refers to the lesser weeverfish. Kleine pietermannen are small, venomous fish that can grow up to 18 centimeters in length. They have a habit of burying themselves in the sand in shallow water, making them difficult to spot. Their dorsal fin and gill covers are equipped with venomous spines. When stepped on, these spines can inject venom, causing intense pain, swelling, and in rare cases, allergic reactions. Most incidents occur when swimmers or beachgoers accidentally step on a hidden fish while wading or playing in the shallows.

How to stay safe at the North Sea beach

The best way to prevent stings from kleine pietermannen is to wear water shoes whenever you enter the water, especially in shallow areas. These shoes provide a physical barrier between your feet and any hidden dangers in the sand.

Staying alert is also crucial. Pay attention to any warning signs on the beach and always listen to advice from lifeguards. Furthermore, it’s important to educate children about the risks. On beaches in Belgium and the Netherlands, you may see signs reading “Opgelet: Giftige pietermannen in ondiep water”. The signs indicate that caution is needed “Attention: Toxic weever fish in shallow water”.

It’s also safer to swim within marked or monitored areas. Many public beaches, beach resorts and municipalities, now install swim zone barriers. These floating barriers, like the Bolina Beach Safety Net Booms and Ecobarrier Jellyfish Safety Nets offered by Ecocoast, can provide an added layer of marine protection. They not only guide swimmers but help local authorities manage safer swimming areas more effectively. In addition, they help keep small watercraft and marine traffic away from designated swimming areas.

What to do if you’re stung by toxic pietermannen

If you’re stung by a kleine pieterman, leave the water immediately to prevent further injury. Familiarize yourself with basic first aid for stings. Rinse the area with hot water (as hot as can be tolerated) – ideally between 40 and 45°C – for at least 30 to 90 minutes. This helps neutralize the venom, and seek medical help if symptoms are severe.

Final thoughts

The increase in toxic pietermannen is a regional challenge across North Sea coastlines. Whether you’re at the beach in Knokke, Renesse or the Danish coast, it’s smart to wear water shoes, swim in marked zones, and stay informed about local beach conditions.

At Ecocoast, we continue to provide reliable solutions like beach safety barriers and floating protection systems that help coastal communities keep swimmers safe and shorelines protected. Stay safe, stay informed, and have a wonderful summer aan de Noordzeekust (on the North Sea coast)!

Interested in protecting your beach or swimming area from marine hazards like giftige pietermannen? Discover our full range of beach and swim safety solutions or contact us today for expert advice.

This news was first reported by the Vlaams Instituut voor de Zee (VLIZ), which confirmed a sevenfold increase in kleine pietermannen along the Belgian coast this summer. Read more: VRT NWS (in Dutch) | VLIZ (in Dutch).

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