Temperatures are rising in lakes across Switzerland, with many seeing record highs due to the recent heatwave. But whilst it might be good news for bathers, it’s less favourable for the country’s natural habitat.
Many lakes across Switzerland were basking in temperatures in excess of 25C at the start of July and in the past two weeks have seen an average increase of 5C in the past fortnight. That represents an all-time record, according to the MeteoNews weather service.
The heatwave that’s been affecting the country for nearly two weeks is largely to blame for the increased water temperatures, but poor snow cover in the mountains at the start of the warm season has also had an impact, MeteoNews explained.
The high temperatures are having a negative impact on fish, the meteorologists say, with some species struggling to cope with the warm waters, as well as lower water levels.
The ‘hot’ water is also harmful to aquatic flora, for which such high temperatures don’t constitute a natural environment.
Warm temperatures and abundant sunlight support algae growth, which can harm fish and other aquatic life.
READ ALSO: Are Switzerland’s lakes warm enough to swim in?
Toxic bacteria
Although algae generate oxygen in sunlight, they consume it too. And large blooms use more than they produce, depleting essential water oxygen levels.
Blue-green algae, a type of bacteria that’s toxic to aquatic life, can also grow in this situation. This bacteria can have a negative impact on water quality and block sunlight, preventing submerged plants from using the light to produce the energy they need to thrive.
It can also be very harmful to dogs and people, so if you see any (it often appears as a paint-like layer on the water rather than the long stringy appearance of normal green algae), make sure you steer clear of the often-foul-smelling blooms.
The flora and fauna are set to get a temporary reprieve as MeteoNews expects temperatures to cool over the coming days, bringing water temperatures back to cooler levels in the short term.
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However, a new high pressure situation could emerge afterwards, bringing further problems, meteorologist Michael Eichmann said on Tuesday.
READ ALSO: What are the rules for swimming in Swiss mountain lakes?
So how hot are lake temperatures right now?
Lake Lugano is the hottest in Switzerland, with its waters currently 28C, five degrees warmer than the 41-year average. Lake Geneva follows closely behind on a balmy 25C.
The temperature at Lake Neuchâtel is also 25C, with Lake Biel and Lake Zurich reaching 26C.
There are over 1,500 lakes across Switzerland, fed by run-off from glaciers and the country’s five major rivers.
The Federal Office for the Environment (BAFU) monitors the lakes daily and records the temperatures. MeteoNews lists current temperatures at the main ones here.
The heatwave has led to sharp increases in river temperatures, too. The Aare near Bern, the Reuss near Lucerne and the Rhine near Laufenburg have all reached record highs.
