The heat wave gripping large stretches of Europe has already been blamed for deadly forest fires and crop failures. Now freshwater fish could be the next victims.

Some regions in Germany sweltered as the temperature hit 39 C and the German Meteorological Office said the country's all-time record of 40.3 C could be topped 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 Deutsche Presse-Agentur (dpa).

In Hamburg, authorities collected almost five metric tons 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.

Young men jump into Lake Lucerne in Switzerland, on Monday. The European weather forecast predicts high temperatures for the next few days. (Urs Flueeler/KEYSTONE via Associated Press)

Scientists say the record heat seen in Europe but also North America and parts of Asia this year points to the influence of man-made climate change and could become more common in the 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.

Farming woes

Meanwhile, the country's farmer are asking the government for one billion euros in financial aid to help cover losses from this year's poor harvest.

Association of farmers president Joachim Rukwied said German farmers expect the grain harvest to be 20 per cent smaller than last year, with rapeseed crops down 30 per cent, as it has barely rained during the past 12 weeks.

A horse rolls on a dry meadow after a long heat wave in Wehrheim near Frankfurt, Germany, Tuesday. (Michael Probst/Associated Press)

A group representing potato farmers expects harvests to be 25 per cent smaller than last year and warned that the losses may lead not only to more expensive but also shorter french fries — because the spuds 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 23 C in some places. Emergency water rescuers told vacationers 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 teens Monday night after the air conditioning in the bus they were travelling in broke down.

Police dogs in the Swiss city of Zurich have been getting special shoes to prevent them from burning their paws on the scorching streets. Swiss authorities have also cancelled traditional fireworks displays in some areas during Wednesday's national holiday celebrations, citing the high risk of forest fires.

Children play in a fountain to cool themselves in a square in Debrecen, Hungary, on Tuesday. The highest degree heat alert has been issued by the Hungarian health authority. (Zsolt Czegledi/MTI via Associated Press)

Across Europe, forest fires have already caused major damage. Earlier this month, 92 people died in Greece from the deadliest wildfire in recent history.

Temperatures of up to 45 C are forecast on the Iberian peninsula from Wednesday and authorities are preparing for temperatures to climb even higher through Sunday, increasing the risk of emergencies.

In Spain, 27 of the country's 50 provinces are at "extreme risk" from heat beginning 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 Monday of 32 C — highly unusual for the Arctic Circle.

Boon for brewers

Some are benefiting from the simmering heat.

Beer brewers in Germany have seen sales rise by 0.6 per cent, or 300,000 hectolitres (7.92 million gallons), in the first half of 2018 compared to the same period last year.

"Especially the alcohol-free types are currently very much sought after," said Marc-Oliver Huhnholz, from the German Brewer Association.

In Denmark, where the Meteorological Institute reported that the month of July has been the sunniest since data started being recorded in 1920, sales of alcoholic beverages dropped in favour of non-alcoholic beers, sodas and white wine, the country's TV2 reported.