# Hazardous marine species in European waters

> Live situation record from CLSTR: https://clstr.news/situations/hazardous-marine-species-in-european-waters
> Updated: 2026-08-03T05:01:00.000Z. Sources: 16. Developments: 5.

In late June 2026 a venomous lionfish was photographed in Montenegro’s Kotor Bay, the first confirmed Adriatic sighting. Experts warned of its ecological threat and painful sting. Throughout July, attention turned to jellyfish. The lion’s‑mane jellyfish (Cyanea capillata), common in the Baltic, North Sea and Mediterranean, was reported off Germany, the UK, Norway, Iceland, Spain and other coasts; its long tentacles can cause burning, welts and itching, especially in sensitive swimmers. The moon jelly remains the most frequent but only mildly irritating. The Portuguese man o’ war (Physalia physalis) was reaffirmed as the most dangerous jellyfish‑like species along European beaches, with thousands of nematocysts delivering intense pain and, rarely, life‑threatening reactions. Authorities issued guidance for recognizing hazardous species and for prompt medical care.

In Spain, lifeguards raised yellow‑flag warnings after several Portuguese man o’ war specimens were found on Gijón’s San Lorenzo, La Escalerona and El Arbeyal beaches; a pilot test using oil‑spill containment barriers is underway to limit their arrival. French Atlantic coasts saw renewed beach closures in early August at Anglet, Ilbarritz, Mimizan, the Basque Country, Landes and Brittany as sightings surged, prompting red or violet flags and advice to rinse wounds with seawater only. Experts link the increased presence of these venomous organisms to rising sea‑surface temperatures, urging continued reporting, culling of lionfish and public awareness to protect swimmers and marine ecosystems.

## Timeline

### 2026-08-03: Portuguese galeae trigger beach closures along France's Atlantic coast

Portuguese galeae sightings have forced beach closures across France’s Atlantic coast; their toxic tentacles cause severe pain and remain dangerous even after death, prompting health warnings and flag bans.

9 sources. https://clstr.news/cluster/portuguese-man-o-war-prompts-beach-closures-along-frances-atlantic-coast

### 2026-07-19: Portuguese man o' war sightings prompt beach warnings in Gijón, Spain

Portuguese man o' war were spotted on Gijón’s San Lorenzo, La Escalerona and El Arbeyal beaches, prompting yellow‑flag warnings and a pilot study using oil‑spill barriers to limit their spread.

2 sources. https://clstr.news/cluster/portuguese-man-o-war-sightings-prompt-beach-warnings-in-gijn-spain

### 2026-07-16: Portuguese Man o' War poses severe risk to European beachgoers

The Portuguese man o' war is the most dangerous jellyfish in Europe, causing severe pain and possible fatality; other species are mostly harmless or cause mild skin irritation.

2 sources. https://clstr.news/cluster/portuguese-man-o-war-poses-severe-risk-to-european-beachgoers

### 2026-07-09: Lion's mane jellyfish pose risks across European coasts

Lion's‑mane “fire” jellyfish and other stinging species threaten swimmers along European and Mediterranean coasts, causing painful reactions despite most jellyfish being harmless.

2 sources. https://clstr.news/cluster/lions-mane-jellyfish-pose-risks-across-european-coasts

### 2026-06-30: Lionfish spotted on Montenegro's Adriatic coast raises health and ecological concerns

A venomous lionfish was photographed near Risan on Montenegro’s Adriatic coast, prompting warnings that its sting can cause severe pain and health issues and that the invasive species threatens local marine b i

2 sources. https://clstr.news/cluster/lionfish-spotted-on-montenegros-adriatic-coast-raises-health-and-ecological-concerns

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Cite as: Hazardous marine species in European waters. CLSTR, https://clstr.news/situations/hazardous-marine-species-in-european-waters