Qu'est-ce que la goutte d'eau et pourquoi est-elle formée ?

A thick layer of algae known as "gošča" has appeared again this year in Lake Bled, raising concerns among scientists and local authorities. The phenomenon, which involves a buildup of cyanobacteria, was confirmed through molecular analysis conducted by the Ciano SLO project. These bacteria were found to contain genes responsible for producing anatoxins, potentially toxic substances. This marks the second consecutive year that such an occurrence has been recorded in the lake, following similar reports last year that sparked public concern after several dogs died under mysterious circumstances. The appearance of gošča in Lake Bled is part of a broader pattern observed in other water bodies across Slovenia. According to Masha Jablonska from the National Institute of Biology, gošča refers specifically to a cluster of microorganisms, primarily algae and cyanobacteria, that initially grow in the form of a biofilm on surfaces such as rocks or submerged plant material. Once mature, these organisms detach from their substrate and float to the surface, forming visible layers on the water's surface. Jablonska explained that there are two distinct types of cyanobacterial blooms: one associated with benthic cyanobacteria, which grow on the bottom of lakes and rivers, and another involving planktonic cyanobacteria, which thrive in the water column. In Lake Bled, the current bloom consists of benthic cyanobacteria, which have previously been identified in other locations such as the Pleterje (Green Lake), Gradisce Lake, and Glinščica near Ljubljana. In contrast, planktonic cyanobacteria typically appear in larger, more uniform patches on the water’s surface, often seen in smaller bodies of water like ponds where nutrient levels are high. Despite the presence of gošča, Jablonska emphasized that its appearance does not necessarily indicate water pollution or excessive tourism. Unlike planktonic cyanobacteria, benthic varieties are not directly linked to nutrient enrichment or extremely high temperatures. The exact causes behind the formation of benthic cyanobacterial mats remain largely unknown, with limited research available on the factors influencing their growth. While human intoxication from benthic cyanobacteria has not been documented globally, precautions are advised, especially for children who might come into contact with the algae. Dogs, however, are particularly vulnerable due to their attraction to the scent of gošča. Last year, several dogs died in Lake Bled, prompting investigations into whether the algae played a role. Although anatoxins were detected both in the algae and within the stomach of at least one deceased dog, further studies are needed to confirm their direct involvement. Another toxin, metaldehyde, was also present in the dog's system, suggesting multiple potential factors. Ingestion of gošča can lead to severe poisoning in animals, with symptoms appearing rapidly and requiring immediate veterinary attention. If a pet exhibits signs of illness after exposure to the algae, owners should inform their veterinarian of the possibility of anatoxin poisoning. The toxins contained within the algae are released into the surrounding water in very low concentrations, making the water itself safe for swimming as long as individuals avoid direct contact with the algae mass. The recurrence of gošča in Lake Bled underscores the need for continued monitoring and research into the environmental conditions that contribute to its formation. Scientists stress that while the phenomenon is entirely natural and widespread across lakes and rivers worldwide, understanding its triggers remains a challenge. Efforts are ongoing to determine how best to manage and mitigate risks associated with this recurring natural occurrence.