At several stretches of the Italian coastline, localised swimming bansare in force at the end of July 2026, triggered by the spread of the tropical microalga Ostreopsis ovata. Individual zones in Apulia, Tuscany, Lazio, Sicily and Liguria are affected, each restricted to clearly defined coastal sections rather than entire regions. As Il Tempo reports, citing Arpa Puglia, the alga, which migrated from tropical waters, is benefiting from the high water temperatures of this summer and is proliferating in calm, well-lit coastal shallows. The situation is being continuously monitored by the regional environmental protection agencies Arpa (Agenzia Regionale per la Protezione Ambientale), which are responsible for environmental monitoring in Italy, and the swimming bans are issued by the relevant local authorities as soon as threshold values are exceeded.
What Ostreopsis ovata is
Ostreopsis ovata is a single-celled dinoflagellate alga, originally native to tropical seas. It has been detectable in the Mediterranean for at least 20 years, most likely introduced via ships' ballast water. The first sightings on the Italian coast were documented in Apulia in the early 2000s. As Open Online summarises in its account of the Arpa Puglia statement, the alga favours calm, warm and well-lit waters and produces toxins that, at certain concentrations, can affect human health.
Its increasing presence is directly linked to the warming of the seas driven by the current fourth heatwave and to climate change more broadly. The conditions favourable to its proliferation include high sea water temperatures, high atmospheric pressure, intense solar radiation and a prolonged period of calm sea, typically in July and August. When the cell concentration exceeds a threshold of around 10,000 cells per litre of water column, an automatic alert protocol is triggered by the Arpa.
Where swimming bans are currently in force
Apulia is the most severely affected region at present. Along the coastal stretch off Molfetta and Giovinazzo, four zones have been classified with red bollini, where cell concentrations have exceeded the threshold. In Tuscany , the Arpa recorded an exceedance at Marina di Pisa on 16 July 2026, and the relevant local authority responded with a localised ban. In Lazio , a ban was in force for several days at Santa Marinella before being lifted following subsequent measurements. In Sicily , the area around Palermo is affected, and in Liguria , the zones of Quinto and Bagnara off Genoa. In Liguria, the non-toxic alga Pyramimonas is additionally present, turning the water a yellowish green without posing any health risks.
An important point of context: all swimming bans issued so far are limited in both geographical scope and duration. There are no large-scale closures of entire coastal stretches, and in most cases bans are lifted after a few days once concentrations fall below the threshold. Nicola Ungaro of Arpa Puglia has stressed in several statements that the presence of the alga does not automatically mean a swimming ban is in place, and that the situation is far from constituting a public health emergency.
Symptoms and when caution is advisable
The toxins produced by Ostreopsis ovata do not act through ingestion but through the inhalation of marine aerosol, which carries the toxins through the air. As Notizie.it summarises in its account of the Arpa recommendations, symptoms such as rhinitis, sore throat, bronchitis, fever, conjunctivitis and skin irritation may occur. The complaints are generally mild and subside within a few days without leaving lasting harm. Bronchospasms may occur in rare cases and require medical attention, particularly in people with pre-existing respiratory conditions.
Caution is especially advisable in two situations: in rough seas along rocky coastal sections, because wave action disperses the aerosol more strongly into the air, and when consuming marine organisms such as sea urchins, which may accumulate the toxins in their bodies. When an Ostreopsis bloom is known to be present, the Arpa recommends avoiding prolonged stays on rocky coastal sections and reducing the consumption of raw or lightly cooked seafood.
What travellers should bear in mind now
For those currently on a seaside holiday in Italy or planning a trip during the upcoming Ferragosto weeks , the situation is no cause for general concern, though it is worth taking a moment to check conditions before entering the water. The most reliable sources are the up-to-date bulletins issued by the relevant regional Arpa and the announcements made by local authorities at the holiday destination. At national level, the Portale Acque of the Ministry of Health offers a map-based overview of all classified coastal sections, where travellers can select their holiday destination directly and view the latest analytical data.
It is also practically useful to look out for red flags and notices posted by local authorities at beaches where bans are active. In the small affected zones, bans are generally clearly signposted and coordinated with the presence of lifeguards. Those looking for alternative bathing options will find suitably cooler choices along the less affected Adriatic sections of Emilia-Romagna, along large parts of the Calabrian and Sardinian coast, and in the mountain regions. The connection with the current heat situation and the broader climatic consequences of this summer makes the Ostreopsis reports one of the many signs of a changing travel reality in the Italian summer.
