Tourists on a seven-mile stretch of Spain's Costa Blanca coast have been banned from entering the sea after the appearance of a rare sea creature with potentially fatal venom.
It is the "Blue Dragon" or Glaucus atlanticus, which contains a powerful venom. Contact with this creature can cause pain, vomiting and dangerous allergic reactions.

The mayor of Guardamar del Segura, Jose Luis Saez, announced the placement of the red flag on the area's beaches, prohibiting swimming until further notice.
He stressed that despite the bright color and small size of 3-4 cm, people should stay away. The municipality launched a preventive operation to monitor possible cells carried by sea currents and asked the public not to touch them, even with gloves, and to notify the rangers or authorities.
Bandera ROJA en las playas de Guardamar PROHIBIDO el BAÑO after the appearance in Playa Vivers of two specimens of Glaucus atlanticus, known as the Blue Dragon. pic.twitter.com/Ksy21uADmO
— José Luis Sáez (@JoseLSaezPastor) August 20, 2025
Vivers Beach, a natural area between the Segura River and La Babilonia Beach, was crowded with people, but few dared to enter the sea, risking heavy fines.
The yellow flag was later placed, allowing swimming with caution near the lifeguard areas.