The heatwave gripping large stretches of Europe has already been blamed for deadly forest fires and crop failures.
Now, freshwater fish could be its next victims.
Some regions in Germany sweltered as the mercury hit 39C, and the German Meteorological Office said the country’s all-time record of 40.3C could be topped on Tuesday.
Rivers like the Rhine and the Elbe have soaked up so much heat that fish are beginning to suffocate.
“I’m expecting a tragedy as soon as next week,” Philipp Sicher from the Swiss Fishery Association told German news agency dpa.
In Hamburg, authorities collected almost five metric tonnes of dead fish from ponds over the weekend, dpa reported. Firefighters have started pumping fresh water into some ponds and lakes in a bid to raise oxygen levels.
Scientists say the record heat seen in Europe, North America and parts of Asia this year points to the influence of man-made climate change, and could become more common in future.
Several of Germany’s nuclear power stations are reducing energy output because rivers used to cool the power plants are too warm.
The low water levels have also made shipping more difficult, with a complete ban imposed on boats on the Oder river in eastern Germany.
Meanwhile, the country’s Farmers’ Association is asking the government for one billion euro (£890 million) in financial aid to help cover losses from this year’s poor harvest.
Association president Joachim Rukwied said German farmers expect the grain harvest to be 20% smaller than last year, with rapeseed crops down 30%, as it has barely rained during the past 12 weeks.
A group representing potato farmers said it is expecting harvests to be 25% smaller than last year and warned that the losses may lead not only to more expensive but also shorter French fries – because the potatoes are so small this year.
The oceans, too, have been affected. Authorities in Poland last week banned swimming at over 50 beaches along its Baltic coast, after hot weather led to the growth of toxic bacteria in the unusually warm sea.
Water temperatures in the Baltic Sea exceeded 23C in some places.
Emergency water rescuers told holidaymakers on hot, sandy beaches – from Swinoujscie in the west to Gdynia in the east – not to enter the sea, where thick, green-brown cyanobacteria colonies have grown and pose a health threat.
Near Wildeshausen, in northern Germany, medics had to attend to a group of about 20 children and teenagers after the air conditioning in the bus they were travelling in broke down.
Police dogs in the Swiss city of Zurich have been wearing special shoes to prevent them from burning their paws on the scorching streets.
In the Alps, helicopters are being used to ferry water to cow pastures where lack of rain and hot weather has left herd's reservoirs nearly empty.
Swiss authorities have also cancelled traditional fireworks displays in some areas during national holiday celebrations, citing the high risk of forest fires.
Across Europe, forest fires have already caused major damage. Earlier this month, 92 people died in Greece – the deadliest wildfire in recent history.
Temperatures of up to 45C are forecast on the Iberian peninsula from Wednesday and authorities are preparing for the mercury to climb even higher through to Sunday, increasing the risk of emergencies.
In Spain, 27 of the country’s 50 provinces are at “extreme risk” from heat beginning on Thursday, the national weather agency said.
In neighbouring Portugal, the general directorate for health warned about dust blowing in from North Africa and authorities said almost 11,000 firefighters and 56 aircraft are on standby to tackle forest fires.
On the other side of the continent, Banak peninsula in northern Norway reported temperatures of 32C – highly unusual for the Arctic Circle.
Some are benefiting from the simmering heat.
Brewers in Germany have seen beer sales rise by 0.6%, or 300,000 hectoliters (7.92 million gallons), in the first half of 2018 compared to the same period last year.
Marc-Oliver Huhnholz, from the German Brewer-Association, said this was a particular boost for “the alcohol-free types are currently very much sought after”.
In Denmark, where the Meteorological Institute reported that the month of July has been the sunniest since they started recording data in 1920, sales of alcoholic beverages dropped in favour of non-alcoholic beers, sodas and white wine, the country’s TV2 reported.