Thousands of small brown jellyfish have appeared off a beach on the Greek island of Evia, drawing attention from residents and visitors after the phenomenon became particularly noticeable in recent hours.

Images from the coastal city of Chalkida show shallow waters densely populated with jellyfish, prompting concern among swimmers and local businesses as the busy summer period approaches.

According to local reports, the jellyfish appeared suddenly, with many observers noting a significant increase in their numbers compared with previous days. The scale of the gathering has transformed parts of the shoreline, creating what many described as a “sea” of jellyfish.

Experts say such outbreaks can be linked to a combination of environmental factors, including prevailing weather conditions, sea currents and rising sea temperatures, all of which may favor the growth and concentration of jellyfish populations.