Lake Garda’s Environmental Health Maintained Despite Algae Challenges
In 2001, there were no yellow-greenish patches on the surface of Lake Garda. This is assured by Chiara De Francesco, environmental quality manager for the Provincia di Trento and detached technician from the analysis laboratory at Forte S. Nicolò (Riva).
The health status of the lake? “All good, but vigilance must not be lowered.” The algae emergency of the last season will not reoccur. Last year, Tarcisio Dagnoli, one of the last fishermen from Limone, sounded an alarm.
Environmental Problems and Fishing
“The indifference surrounding Lake Garda is incredible, despite it being the main source of income for thousands of people. Tourism has enriched those who were once farmers or fishermen,” he said. “Yet, all towns dump wastewaters into the waters, and algae proliferate. Previously, algae developed for thirty days; now, they last for several months, preventing many fish species from feeding on their natural food: plankton.”
Fishing has also become challenging: a few hours after casting the nets, it is difficult to retrieve them, as the vegetation has grown heavily into the nets. Furthermore, the water is constantly murky: impossible to see beyond 40-50 centimeters depth. As if that wasn’t enough, all the conditions have changed.”
In the past, sandy materials would settle on the seabed and clean it, promoting the deposition of fish eggs. The trout has disappeared. There are no longer the “freghe” (sandy beds where fish lay eggs) of vairons, scardole, tenches, and brown trout.
Invasion of Species and Environment
The perch population fluctuates. Conversely, there is a true invasion of bleak (cavedani), which some compare to rats on land and seagulls in the sky. Under the stones, the “saiòtti”—tiny shrimps—are no longer found.
As for birds, legionary populations of cormorants and coots have arrived and started nesting. Vincenzo Ceschini, geologist and vice-president of the Garda Community and environmental researcher, responded that the overall situation was rather good.
“Our lake is the largest in Italy (about 369 km²), with the greatest volume of water (49 billion cubic meters). A large reservoir that will likely be used in the future to supply water to the aqueducts of the Po Valley. The limnological investigations carried out on the Trentino shore and in the lower lake—both on the Brescia and Veronese sides—provide a detailed and scientific overview of the situation.”
“The substances responsible for eutrophication, such as ammonia, phosphorus, nitrites, and nitrates, are well below legal limits,” assured Ceschini. “Transparency, measured with a Secchi disk, ranges from a minimum of 6 meters to a maximum of 16; chlorophyll values range from 2.4 to 3.6 µg/l. Lake Garda, one of the cleanest lakes in the world, is essentially oligo-mesotrophic, meaning it contains few substances that could provoke eutrophication and thus poor water quality.”
This condition is supported by the network of purification plants, such as the one in Peschiera, which collects wastewater from the lakeside towns. Of course, it must always be kept in mind that the renewal time is about 25 years, and uncontrolled sewage discharges (as well as those from agricultural and artisanal activities) represent a constant danger to be immediately reported.” The “crazy algae” phenomenon (Anabaena) emerged fully in summer.
A greenish, slightly gelatinous mass spread across the surface, in marinas or near beaches. It has the same color as yellow flour when it is poured cold into a pot, and not yet solidified by heat. An unpleasant mucilage, both ugly to look at and even worse to smell.
The reason? “The waters from the seabed, including those at less than 350 meters depth—known to be richer in ‘nutrients,’ phosphates, and nitrates, which are highly attractive to microalgae—have risen to the surface. As a result, the algae multiplied. The peculiarity is that such overturning events are usually cyclical, occurring every seven to ten years.”
Instead, after the last episode in 1992, others were recorded in 1999 and 2000. Nonetheless, experts assured that these are not signs of pollution. A curious physical phenomenon, known as “sessa,” involves the oscillation of the entire water mass, which lifts from one side and lowers on the opposite, with subsequent inversion of positions.
