July 3, 2025, 2:45 pm | Read time: 5 minutes
When vacationers head into the water, they often take a quick look at the ocean floor—and for good reason. In several European vacation spots, there are marine creatures best avoided. TRAVELBOOK, in collaboration with biologist Ulrich Karlowski, explains where caution is advised.
Whether it’s Italy, Croatia, or the Baltic Sea, for many, a summer vacation by the sea is a must. But anyone spending a day at the beach should not only think about sunscreen and enough water but also stay alert while swimming. The sea is home to some creatures you’d rather avoid. They can sometimes cause unpleasant skin rashes, burning, or even poisonous stings.
Overview
Do Not Touch! ‘Blue Dragon’ Spotted Off Mallorca’s Coast
“Red Tide” Threatens the Coast of Florida! Danger for Beach Visitors
This Is the Most Venomous Island in the World
These Potentially Dangerous Sea Creatures Exist in Europe
Sea Urchins
They are round, black, and equipped with numerous sharp spines: Sea urchins are among the marine creatures you’d rather not encounter while swimming. Those who vacation in Croatia are familiar with them, especially in rocky bays. But they are also common in other Mediterranean countries such as Greece, Italy, or Spain. Stepping on a sea urchin can be quite painful, as the spines penetrate deeply into the skin and often leave residues that can become inflamed. “Going barefoot into the water is not a good idea,” says marine biologist Ulrich Karlowski from the Marine Conservation Foundation in an interview with TRAVELBOOK. To be on the safe side, you should get closed water shoes, which are often available in beach shops and the like.
If you do step on a sea urchin, you should carefully remove visible spines and then disinfect the wound. Generally, contact with a sea urchin is painful but mostly harmless. However, in cases of severe swelling, persistent pain, or inflammation, it is advisable to see a doctor.
Jellyfish
Several species of jellyfish are found in European waters. Some are harmless, while others can cause unpleasant skin reactions. According to experts, jellyfish currently pose the greatest danger to beachgoers in Europe, as they are expected to appear in larger numbers due to the warming of the Mediterranean Sea. Although contact with fire and sail jellyfish is generally not fatal, it can be dangerous, especially for people with pre-existing conditions. To protect yourself, the expert advises keeping a lookout and, if necessary, moving away quickly.
Other species that can be dangerous to humans include the pink to purple shimmering luminous jellyfish. It can cause burn-like injuries upon contact. These approximately 12-inch creatures are mainly found in the Mediterranean during the height of summer. According to the German Marine Conservation Foundation, the venom of the so-called fire jellyfish is generally not acutely hazardous to health, but pain and discomfort can occur up to two weeks after contact with the jellyfish.
Weeverfish
The weeverfish feels at home in the North Sea, along the Adriatic coast, and in the Mediterranean. The name sounds harmless, but this perch-like fish is considered one of the most dangerous sea creatures in Germany. Caution is especially advised in shallow water and on sandy ground. As PETBOOK reported, the weeverfish buries itself in sand or silt while hunting. In the summer months, it moves closer to the shore to spawn, leading to more frequent encounters with swimmers. A sting from the spines on its dorsal fin can cause severe pain, swelling, and in rare cases, even circulatory problems. Again, water shoes can help prevent painful incidents.
Similar to sea urchins, if you come into contact with a weeverfish, the spines should be carefully removed. Additionally, it can help to treat the affected area with hot water first and then cool it.
Blue Dragon
The Blue Dragon, also known as the Blue Angel, not only has an impressive name but also looks spectacular. The blue sea slug indeed resembles a small dragon. However, as beautiful as it appears, it can be quite dangerous to humans. The creature feeds on venomous jellyfish like the Portuguese Man o’ War, stores their stinging venom, and can pass it on upon contact. This can lead to severe skin reactions such as rashes, redness, or swelling. Originally, this marine creature is native to warm waters, such as those off Australia, South Africa, Hawaii, or in the Caribbean. In recent years, however, the Blue Dragon has been increasingly spotted in European coastal regions.
As with all marine animals, the sea and beach are primarily the habitat of the animals, not humans. As fascinating as the Blue Dragon looks, it’s best not to touch it and simply leave it alone.
In addition to marine animals, some waters also contain algae species that can cause discomfort. “We also have some in the Baltic Sea, like red algae, which can be painful upon skin contact and cause skin irritation. In such cases, you should avoid going into the water,” explains marine biologist Karlowski. If there is an increased algae presence, the affected beaches usually issue timely warnings.