Toxic beach hazard threatens to ruin Italian holidays for millions of tourists

With over 170 million tourists expected to flock to Italy's beaches over this summer season, the southern European country is one of the top holiday destinations worldwide. While neighbouring countries France and Spain are having to grapple with raging wildfires this holiday season, Italy is facing an invisible yet toxic summer beach hazard that has been quietly growing for years.

Ostreopsis ovata, a toxic microscopic dinoflagellate, which is a type of algae that began appearing on Italian coasts in the 1990s as a tropical curiosity, has now reached emergency-threshold concentrations at multiple monitored sites in some of the country's most favourite holiday destinations, as highlighted by the Tech Times outlet.

From Puglia to Liguria on the Mediterranean shores, ranging all the way to the Po River and spreading into inland lakes, the situation has forced the government's environmental protection agency (ARPA) to include several sites into the highest tier in the agency's alert system. 

The numbers at two of those sites have already crossed Italy's legally significant threshold, with the water samples from Torre Canne and Prima Cala in Molfetta having recorded cell growth levels above the 30,000 cells/liter level at which Puglia's local branch of ARPA is required to notify the regional government, with the latter even showing levels three times higher than the cut-off limit.

Two other red-flagged sites are Giovinazzo (24,473 cells/liter) and Porto Badisco near Otranto in the Lecce province (25,440 cells/liter), which currently sit just below the emergency trigger but in the range that typically precedes bloom intensification.

However, the bloom of this toxic alga has spread to other regions as well, including the Ligurian coast, where many popular coastal towns, such as Portofino and the Cinque Terre chain that form the Italian Riviera. For now, Ostreopsis has been confirmed to be present along the Genoa coastline in July 2026, with its standard summer monitoring program tracking conditions at 16 sites across Liguria.

This also includes a stretch of Genoa coast that, in early July 2025, saw three 20-year-old women hospitalised with erythema, fever, swelling, and disorientation after swimming there. This incident illustrated the characteristic symptom cluster of Ostreopsis exposure, with the current alert including the same risk conditions.

What makes it so hazardous

Most other beach toxins pose a health risk from contaminated water, which can accidentally be swallowed by people entering the water. However, Ostreopsis ovata does not work that way as one can get exposed to the toxic algae simply by walking along the beach or being close to the shoreline. 

That is because the organism is benthic, meaning it lives not in the open water column but is attached to rocks, macroalgae, and sandy sediment near the seafloor. Under bloom conditions, water waves lead to these dense cell masses detaching and breaking apart, which releases fragments of the toxin into sea spray and marine aerosol. According to Italy's National Institute of Health (ISS), this aerosol can then be inhaled not only by swimmers but by anyone walking or resting near the shoreline, and the risk intensifies on windy days when spray is being carried further inland.

Back in 2005, similar algae caused 200 people to require a visit at first-aid stations, while 20 had to be hospitalised for one to three days. This affected residents and visitors who were simply standing on the shore, with symptoms such as rhinorrhea, cough, fever, bronchoconstriction, mild difficulty breathing, and in some cases conjunctivitis reported. 

An additional layer of concern is that a 2022 study identified two entirely new families of toxins from a Mediterranean strain of Ostreopsis — named liguriatoxins and rivieratoxins — whose full chemical arsenal is still being characterised by scientists. The danger lies in the fact that current monitoring and public health guidance are calibrated to known palytoxin derivatives and do not capture information on those new strains. 

How to protect yourself

The official guidance by Italian public health authorities includes watching out for symptoms that contact with the toxic algae often causes, which include skin rashes, difficulty breathing, and red or irritated eyes. While they point out that the toxin is not lethal at typical exposure levels, symptoms can require hospital monitoring, particularly in people with asthma, chronic lung disease, or cardiovascular conditions, as well as children and elderly individuals.

By Nazrin Sadigova