English: Averno is a Lake in the Campania region in Southern Italy, close to Naples. It is known for its characteristic landscape and biodiversity and is one of the Natura2000 protected areas of the Regional Park of Campi Flegrei. Recently, its waters have turned red as a result of a massive algal bloom, as reported by local media. These images, acquired by the Copernicus Sentinel-2 satellites on 1 March 2022 (left) and 5 April 2022 (right), show the remarkable change of colour of the Averno Lake’s waters. Scientists who are currently monitoring the phenomenon believe that the dark-red colour is caused by an algal bloom in the lake and by the eutrophication of the lake water (that is, the accumulation of nutrients in bodies of water), which is influenced by weather conditions. This temporary change in colour occurs seasonally, and the Averno Lake should soon go back to normal. Data from Copernicus missions allow the detection and monitoring of different algal blooms and of lake water quality levels, which are essential for the protection of vulnerable environments and biodiversity sites.