Despite the recent bout of thunderstorms, officials across the country have recorded bath-like temperatures in lakes in Switzerland. Some, like Lake Zurich and Lake Lugano, are now warmer than the sea in top Mediterranean destinations.
Across the country, the bright sunshine and 30-degree temperatures have super-heated Switzerland’s lakes and rivers. According to the Water Research Institute at ETH Zurich (Eawag), the temperature in Lake Zurich rose to 28,4 degrees celsius by the afternoon of August 13, a near-record.
The organisation noted that Lake Zurich has only been warmer than 28 degrees for 11 days in the last 15 years. Elsewhere, lakes in Geneva, Constance, Neuchâtel, Maggiore, Zug and Biel / Bienne all reported balmy conditions of around 25 degrees on August 14, with temperatures in Lake Lugano peaking at 29 degrees.
These tropical temperatures are now equivalent to the water temperatures seen in top Mediterranean destinations. According to 20 Minuten, on August 13 the water was 29 degrees in Palma de Mallorca, 27 degrees in Barcelona, 27 in Cagliari and 26 in Limassol.
Those craving the warmest temperatures should head to small lakes in Switzerland. Eawag predicted that by Friday, the Egelsee, Greifensee, Lützelsee and Katzensee will all warm up to above 29 degrees. Even Swiss rivers have heated up, with the Rhine (24,6 degrees), Thur (24,3) and Rhône (26,5) all reporting above-average temperatures.
While the high temperatures are good news for swimmers who want to indulge in a summertime dip, the impact of the heat is a mixed bag for Swiss wildlife. Speaking to 20 Minuten, the head of the office for waste, water, energy and air in Canton Zurich Katharina Weber explained that warmer lakes are not a huge issue for the creatures that live there. "In the lake, fish that prefer cooler water can dive into deeper layers where the temperatures are lower," she noted.
Things are more complex in rivers, with Weber noting that any temperatures above 22 degrees put great stress on cold-water-loving species like trout and grayling. These fish typically tend to gather around cooler streams or migrate to colder rivers. However, she assured that the phenomenon is not harmful in the short term.
Finally, Weber confirmed that they are “not aware of any major blue-green algae blooms” - the algae which can be harmful to pets if consumed. She noted that blue-green algae only tends to bloom in large quantities if the start of the summer is hot and dry, meaning 2024 will likely see less of the plant grow due to how wet and dark it was at the start of the season.
Nevertheless, she noted that blue-green algae can appear at short notice. "It is therefore always advisable to look for signs of blue-green algae - cloudy and discoloured water, flakes, streaks or a greasy film on the water - before swimming or when taking your dog near water, and to avoid such places."
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