Lake Mucilage Mystery: Unprecedented Green Algae Found in Riva Harbor

Remo Cattoni has spent 48 of his 62 years renting boats (and now pedal boats) in the Brolio harbor. But in almost half a century of daily visits to this tiny lake inlet, a shelter for boats since time immemorial, he has never seen a phenomenon like the one unfolding in front of him over the past three to four days.

The mystery of the lake mucilage

Carried by waves and currents, every morning a greenish and slightly gelatinous mass accumulates in the harbor, composed of many tiny filaments and granules suspended in the water. “Is this lake mucilage?” – wondered the Rivana dock visitors.

It could be, because certainly – also considering the smell of rotten eggs rising from the water’s surface – the phenomenon is organic in nature: according to Cattoni himself and other lake observers, it is not excluded that it might be a type of algae never seen before.

Aside from its color (which, as mentioned, tends toward green, a pea green), the new visitor on the Rivana side of the lake – which also penetrates the Rocca canal and the harbor at Piazza Catena; some say they’ve also noticed it in Torbole harbor – resembles the yellow flour when it is poured cold into a pot and has not yet solidified from the heat of the flame.

Analyses and hypotheses about the phenomenon

To uncover the mystery of this ugly-looking sludge, we asked for insights yesterday from Dr. Chiara De Francesco, of the provincial analysis laboratory at Porto San Nicolò.

“We collected samples last Friday,” she told us, “They are indeed from a unicellular algae, Anabaena, which has always been present in the lake. The patches had been observed in the lower Garda before. But in Riva, they are a novelty, probably linked to particular climate conditions.

It is a phenomenon to watch carefully, without a doubt, and one that needs clarification. We will try to understand the reasons for this anomaly,” she added.