Swiss Authorities Warn Against Blue-Green Algae In Lake Lugano

(MENAFN- Swissinfo) The Swiss canton of Ticino is advising against swimming in the southern basin of Lake Lugano, due to blue-green algae, which are toxic to humans and animals. This content was published on September 5, 2025 - 13:46 3 minutes Keystone-SDA

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Significant exposure to the algae and can cause skin reactions, gastrointestinal complaints or even liver problems.

Between the Gulf of Riva San Vitale and the lake dam at Melide, Lake Lugano the water is once again partially yellow-green instead of blue. The reason is blooms of cyanobacteria, as blue-green algae are known in technical jargon.

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The phenomenon has intensified in recent days and the blue-green algae have spread as far as the Gulf of Agno, the Ticino cantonal chemist announced on Friday.

Swimming in Lake Lugano is therefore not recommended where there are dense and extensive blooms that resemble a carpet. According to the cantonal chemist, cyanobacteria are present in high concentrations in these areas and pose a high risk to humans and animals. Typical for such a high occurrence of blue-green algae is also a turbidity of the water.

If a section of the lake is only partially infested with blue-green algae, there is a medium risk. Swimming in such areas is not recommended for people with sensitive skin, small children and animals.

The Ticino authorities therefore recommend swimming only in clear water at a visibility depth of one to two metres and avoiding visible accumulations of cyanobacteria. After swimming, people should shower and dry your skin thoroughly.

Information signs in the lidos

According to the cantonal laboratory's protocol, the affected municipalities and lidos have put up appropriate signs at most access points to the water, the press release continues. A flag system is also used on monitored beaches to indicate the level of danger.

The main cause of these blooms is the massive proliferation of Microcystis, a genus of cyanobacteria that can produce toxins. Blooms of this type are favoured by nutrient input into the lake and high temperatures. They typically occur in the second half of summer.

Translated from German with DeepL/mga

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