Complete mixing of the waters: Lake Garda breathes again

05 May 2026

 

At the beginning of last month, a rare and long-awaited event—absent for two decades—was recorded in Riva del Garda.
The probe of the Provincial Agency for Environmental Protection of Trento (APPA), positioned between Punta Lido and Sabbioni beach, recorded a temperature of 9.45 °C at one meter depth in early April, almost perfectly matching the temperature measured at 270 meters depth on February 24.

This elimination of the temperature—and therefore density—difference between surface and bottom layers created a state of homothermy.
This is a rare condition for Lake Garda, which is considered an oligomictic lake (meaning it fully mixes only in certain years), and it occurred at exactly the right moment: alongside the cold, a strong northerly wind swept through Trentino, triggering convective motion responsible for the movement of lake waters.

The combination of these elements initiated a complete mixing of the lake waters—something that had not happened in Lake Garda since 2006.
In deep lakes, partial mixing is far more common, as full mixing is harder to achieve. However, the perfect weather conditions made this extremely important event for the lake’s health possible.

What happened in practice? Deep waters rose to the surface, exchanging with surface waters.
As a result, nutrients and microelements that had settled on the lakebed were brought up, while the bottom layers were replenished with oxygen from above.

Data from the APPA probe showed oxygen levels increasing from 6.61 mg/l on February 24 to 8.80 mg/l on April 1.

Water oxygenation is a very important parameter because:

“[…] The presence of oxygen at different depths in a lake is essential for species development. The euphotic zone—those layers reached by sunlight—allows algae to carry out photosynthesis and produce the oxygen necessary for other aquatic life. The aphotic zone, by contrast, does not receive sunlight, preventing photosynthesis. In these layers, oxygen is only consumed through animal respiration and the decomposition of organic matter.

The circulation of deeper water layers is essential to supply oxygen even to zones without vegetation. Monitoring oxygen levels at greater depths is crucial, as it is the element that sustains animal life in the aphotic zone.”
(https://www.appa.provincia.tn.it/News/Approfondimenti/Le-principali-componenti-chimico-fisiche-dei-laghi#)
 

This is excellent news that reassures us about the lake’s health: thanks to this natural restoration process, Lake Garda is breathing again.