First cyanobacteria blooms in the southern basin of Lake Lugano

Ticino's bathing waters remain of good quality. In the southern basin of Lake Lugano, however, the season's first cyanobacteria blooms have appeared.

July's checks covered 82 monitoring points. The network takes in Lake Maggiore, Lake Lugano and the lake of Astano, along with the Ticino, Moesa, Verzasca and Maggia rivers. The microbiological analyses returned positive results. The data can be consulted on the page of the Environmental Observatory of Italian-speaking Switzerland, run by the Department of the Territory. A further round of sampling is planned for August.

Since the end of July, some light blooms have been observed in the southern basin of Lake Lugano. The cantonal laboratory has intensified monitoring in line with the established protocols. Municipalities and those running supervised beaches have been notified and asked to follow developments, putting up information signs if needed.

For now the presence remains limited. The authorities nonetheless recommend checking the water by eye before going in.

Why the situation changes within hours

Cyanobacteria are micro-organisms normally found in lakes and rivers, once wrongly called blue-green algae. Their growth is encouraged by a high nutrient content, by still water and by the alternation between settled warm spells and storms that carry fresh nutrients into the lake.

When growth becomes excessive, surface blooms appear that are visible to the naked eye, forming green or yellow mats. According to the canton, these accumulations can move with the wind or the currents and affect different parts of the basin within the same day, particularly in the bays. A beach that is clear in the morning may look different by the afternoon.

Some species produce toxic compounds. The risk to people and animals rises with the density of the bloom, and contact with visible formations should be avoided.

High concentrations can cause allergic skin reactions, gastrointestinal complaints or liver damage. Small children are more exposed, because they swallow water without noticing while playing. The same applies to animals, and to dogs in particular.

The phenomenon arrives in a season marked by prolonged heat and scarce rainfall. Those are the conditions that leave the water warmer and stiller, which is what cyanobacteria exploit best.