Anyone currently planning to enter the water on the beaches of the Bassin d’Arcachon or along Gironde’s Atlantic coast often first takes a careful look at the sea. In recent days, there have been increasing reports of unusually large jellyfish being spotted near the shore. Some holidaymakers are therefore choosing not to swim, while others prefer to observe these fascinating animals from the beach. The sight is impressive, but in most cases there is a common natural phenomenon behind it.
During the summer months, jellyfish regularly drift from the open Atlantic towards the coast. The cause is the interaction of wind, tides and currents. Especially after prolonged periods of westerly winds, jellyfish are pushed towards the beaches and gather in sheltered bays or shallow coastal areas. Around Arcachon, this spectacle can be seen almost every year — sometimes more intensely, sometimes less so.
The current weather conditions are further intensifying this phenomenon. Calm seas and relatively warm surface water mean that jellyfish remain near the coast for longer. Instead of quickly drifting back out to sea, they often stay close to the beaches for several days. This is precisely why they are particularly noticeable to holidaymakers at the moment.
The high temperatures of recent weeks may also have played a role. Many jellyfish species grow faster in warmer water, and favorable conditions promote population growth. Nevertheless, marine biologists do not believe that every year with many jellyfish can be attributed solely to climate change. Populations naturally fluctuate greatly. Ocean currents, food supply, and breeding success also play a decisive role.
But why do jellyfish cause so much concern? Mainly because of their size. Some specimens reach bell diameters of several tens of centimeters and have long tentacles that seem to stretch endlessly through the water. Encountering such an animal while swimming can quickly cause fear — which is entirely understandable.
However, being large does not automatically mean being dangerous. Some commonly seen species cause only mild skin irritation, while others sting much more painfully. That is why lifeguards generally advise against touching jellyfish — whether in the water or on the beach. Even specimens washed ashore often still have active nematocysts (stinging cells) and can cause painful injuries. One thing is clear: do not touch them.
Despite many sightings, swimming bans have not been imposed on most beaches. Local lifeguards are monitoring the situation closely and inform visitors when large groups of jellyfish are drifting near the coast. If you want to swim, you should still be cautious. Jellyfish can usually be easily avoided by turning away, children in particular should be watched closely, and in the event of a sting, it is recommended to rinse the affected area with seawater. If symptoms persist or become more severe, it is safer to seek medical attention.
Jellyfish swarms have long been part of the Atlantic’s natural rhythm and occur regularly, especially between June and August. The reason they may be more noticeable this summer is probably that many people are flocking to the beaches at the same time and sightings are shared on social networks within minutes. Everyone has probably had such an experience.
So there is no reason for holidaymakers to interrupt their swimming holiday. With a little caution and an appropriate distance from marine life, there is generally nothing to stop you from enjoying a day on the Atlantic. Often, the wind direction changes after just a few days — and with it, the jellyfish disappear from the swimming areas.