Firefighters from across Europe struggled Thursday (local time) to contain a huge wildfire in France that has swept through a large swath of pine forest, while Germans and Poles faced a mass fish die-off in a river flowing between their countries.

Europe is suffering under a severe heat wave and drought that has produced tragic consequences for farmers and ecosystems already under threat from climate change and pollution.

The drought is causing a loss of agricultural products and other food at a time when supply shortages and Russia's war against Ukraine have caused inflation to spike.

In France, which is enduring its worst drought on record, flames raged through pine forests overnight, illuminating the sky with an intense orange light in the Gironde region, which was already ravaged by flames last month, and in neighbouring Landes. More than 68sq km have burned since Tuesday.

Firefighters tackling a blaze near Saint-Magne, south of Bordeaux, southwestern France. Photo / Fire brigade of the Gironde region

The French wildfires have already forced the evacuation of about 10,000 people and destroyed at least 16 houses.

Along the Oder River, which flows from Czechia north into the Baltic Sea, volunteers have been collecting dead fish that have washed ashore in Poland and Germany.

Piotr Nieznanski, the conservation policy director at WWF Poland, said it appears that a toxic chemical was released into the water by an industry and the low water levels caused by the drought has made conditions far more dangerous for the fish.

"A tragic event is happening along the Oder River, an international river, and there is no transparent information about what is going on," he said, calling on government authorities to investigate.

People living along the river have been warned not to swim in the water or even touch it.

Dead fish have washed up along the banks of the Oder River between Germany and Poland, and people have been warned not to swim in the water, or even touch it. Photo / AP

Poland's state water management body said the drought and high temperatures can cause even small amounts of pollution to lead to an ecological disaster but it has not identified the source of the pollution.

In northern Serbia, the dry bed of the Conopljankso reservoir is now littered with dead fish that were unable to survive the drought.

The water level along Germany's Rhine River was at risk of falling so low that it could become difficult to transport goods — including critical energy items like coal and gasoline.

In Italy, which is experiencing its worst drought in seven decades, the parched Po River has already caused billions of euros in losses to farmers who normally rely on Italy's longest river to irrigate their fields and rice paddies.

"I am young and I do not remember anything like this, but even the elderly in my village or the other villages around here have never seen anything like this, never ever," said Antonio Cestari, a 35-year-old farmer in Ficarolo who says he expects to produce only half his usual crops of corn, wheat and soy because his river-fed wells have such low water levels.

The Po runs 652km from the northwestern city of Turin to Venice. It has dozens of tributary rivers but northern Italy hasn't seen rainfall for months and this year's snowfall was down by 70 per cent. The drying up of the Po is also jeopardising drinking water in Italy's densely populated and highly industrialised districts.

The dried riverbed of the Po river in Sermide, Italy. Photo / AP

Over in Portugal, the Serra da Estrela national park was also being ravaged by a wildfire. Some 1500 firefighters, 476 vehicles and 12 aircraft were deployed to fight it but the wind-driven blaze 250km northeast of Lisbon was very hard to reach, with inaccessible peaks almost 2000m high and deep ravines. The fire has charred 10,000ha of woodland.

In Britain, where temperatures hit a record 40.3C in July, the weather office has issued a new warning for "extreme heat" from Thursday through Sunday, with temperatures forecast to reach 36C.

It has been one of the driest summers on record in southern Britain, and the Met Office weather service said there is an "exceptional risk" of wildfires over the next few days.

London Fire Brigade said its control room had dealt with 340 grass, garbage and open-land fires during the first week of August, eight times the number from last year.

Assistant Commissioner Jonathan Smith said, "The grass in London is tinderbox dry and the smallest of sparks can start a blaze which could cause devastation."

In Switzerland, a drought and high temperatures have endangered fish populations and authorities have begun moving fish out of some creeks that were running dry.

In Hausen, in the canton of Zurich, officials caught hundreds of fish, many of them brown trout, in the almost dried-up Heischerbach, Juchbach and Muehlebach creeks this week by anesthetising them with electric shocks and then immediately placing them in a water tank enriched with oxygen, local media reported. Later, the fish were taken to creeks that still carry enough water.

Large areas of grass have turned yellow due to the dry conditions in Holyrood Park, Edinburgh, Scotland. Photo / AP

Despite all the harm caused by the extreme weather, Swiss authorities see one morbid upside: they believe there's hope of finding some people who went missing in the mountains in the past few years because their bodies are being released as glaciers melt.

In the Swiss canton of Valais, melting glaciers have recently revealed parts of a crashed airplane and, at separate locations, at least two skeletons. The bodies have not yet been identified, news website 20Minuten reported Thursday.

Spanish state television showed dozens of trucks heading to France having to turn around and stay in Spain because wildfires had forced authorities to close some border crossings. TVE reported that truckers, many carrying perishable goods, were looking for ways to cross the border because the parking areas around the Irun crossing were full.

France this week is in its fourth heat wave of the year as it faces what the government describes as the country's worst drought on record. Temperatures were expected to reach 40C on Thursday.