Many Swiss lakes hit record temperatures for May

Warm lake temperatures: good for water sports, not always so good for ecosystems. Keystone-SDA

Some 26 of the country’s 32 largest lakes have seen surface temperatures never before recorded at this time of year, the Tages-Anzeiger has reported.

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Lakes Zurich, Geneva, Maggiore, Lucerne and Brienz are all affected, the Tamedia-group newspaper wrote on Saturday.

On Saturday, several lakes far exceeded the 20-degree mark, with some high points reaching almost 25°C. Warmest was Lake Murten at 24.6°C. Close behind was Lake Geneva, which saw 23.6°C, while Lake Zurich hit 22.4°C. Lake Maggiore in southern Switzerland recorded 21.8°C. Slightly cooler, but still well above seasonal averages, were Lake Lucerne and Lake Biel (both 20.3°C).

High water temperatures can have unpleasant consequences for bathers: blue algae, bacteria and duck fleas (cercaria) are more present in warm water. “In future, cercaria are very likely to spread to many lakes in late summer,” Martin Schmid, a researcher at the Swiss Federal Institute of Aquatic Science and Technology (Eawag), told the Tages-Anzeiger. The tiny larvae can cause an allergic reaction and severe itching in humans.

Fish fauna are also affected. “The warming of the water poses a considerable threat to life in the lake,” said Martine Rebetez, a climatologist at the University of Neuchâtel. Salmonids, a group including trout and char, suffer: they need cool, oxygen-rich water and can die if temperatures exceed 20°C for a long period.

“Their growth is already impaired after around 15°C,” Rebetaz told the Tages-Anzeiger.

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Adapted from Italian by AI/dos

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