Swiss residents navigating the fourth heat wave of the year face extreme conditions as temperatures exceed 30 degrees, pushing water levels in Swiss rivers and lakes to historic lows, according to economic editor Patrik Berger. In Zurich, this intense heat has triggered a visible outbreak of blue-green algae, known scientifically as cyanobakterien, on the surface of the Limmat river at the popular Oberer Letten open-air river bath.
The kantonale Baudirektion confirmed that slimy green patches, locally referred to as toad skins or "Krötenhäute", have formed across the water's surface and around entry points. While these organisms typically grow out of sight at the bottom of flowing waters, low water levels in the Limmat allow unusually high amounts of sunlight to penetrate the bed. This exposure promotes rapid growth, ultimately driving the cyanobacteria upward.
Did You Know?
The low water levels impacting the Limmat extend across the region, causing the water level of the Zürichsee to reach a record low while rivers like the Töss near Winterthur have remained completely dry for days.
Health Risks and Safety Measures in Zurich
Although the name suggests standard vegetation, cyanobacteria can synthesize toxic compounds capable of causing skin irritation, vomiting, and respiratory distress, as outlined by the ETH water research institute Eawag. Small children and dogs face the highest risk, as swallowing even minute amounts can lead to severe illness or prove fatal in extreme cases. Despite these hazards, the Zürcher Sportamt has kept the bathing facilities open, maintaining that the overall water quality remains satisfactory.
To mitigate potential health impacts while swimming continues, officials have erected informational signage at the site. Visitors are advised to steer clear of visible algae accumulation, swim exclusively in clear water areas, avoid swallowing river water, and take a thorough shower immediately after exiting the bath.
Broader Impact Across Swiss Cantons
The unusual meteorological conditions are affecting water bodies well beyond Zurich. Back in mid-June, authorities in Ticino issued warnings regarding blue-green algae in the Lago Maggiore close to Muralto. Concurrently, other regional administrations, including the canton of Solothurn and the canton of Basel-Landschaft, distributed general warnings to the public about similar bacterial developments.
Frequently Asked Questions
What are the slimy green layers appearing on the Limmat?
The slimy patches, locally called toad skins, consist of cyanobacteria, which are commonly misidentified as blue-green algae and normally remain hidden at the bottom of flowing bodies of water.
Is it still safe to swim in the Oberer Letten river bath?
Yes, the bathing facility remains open and the water quality is considered acceptable, provided visitors follow safety instructions such as avoiding algae patches, avoiding swallowing water, and showering after swimming.
Who is most at risk from the cyanobacteria?
Small children and dogs face significant risks because ingesting toxic substances produced by certain strains of these bacteria can cause skin irritation, vomiting, respiratory issues, and potentially fatal outcomes for animals.
Do you plan to change your swimming habits in local rivers during the current heat wave?