A massive outbreak of venomous purple jellyfish is spreading rapidly across popular Greek sea areas, including the Sporades islands and the Pagasetic Gulf, prompting marine experts and health authorities to issue urgent warnings to swimmers at the height of the summer season.
The Hellenic Biodiversity Observatory said Monday that the scale of the bloom was initially underestimated but has now become a significant concern.
Dense swarms of the jellyfish, known scientifically as Pelagia noctiluca, have been confirmed along the coasts of the Euboean and Thermaikos gulfs and on the tourist-heavy islands of Skiathos and Skopelos.
The jellyfish, recognizable by its purple hue and long tentacles, delivers a painful sting that can cause intense burning, redness, and swelling.
While generally not life-threatening, the stings can trigger more severe reactions in sensitive individuals.
Health authorities are advising anyone who is stung to immediately rinse the affected area with seawater, not fresh water, and to carefully remove any remaining tentacles with a flat object like a credit card, not with bare hands.
Scientists say the current outbreak mirrors a wider phenomenon across the Mediterranean in recent years, linking the population booms to rising sea temperatures and overfishing of the jellyfish's natural predators.
The Biodiversity Observatory is urging the public to help track the outbreak in real-time by reporting sightings through the iNaturalist mobile app, which allows experts to monitor the spread and issue more accurate warnings.