The Met Office has confirmed June was the hottest on record in UK history, according to provisional figures.
The average temperature for June 2023 hit 15.8C, 0.9C hotter than the joint previous record of 14.9C in 1940 and 1976, according to the forecaster’s provisional figures.
In total, 72 counties saw their hottest June since records began in 1884.
Mark Owen, Angling Trust head of fisheries, warned that the hot weather had already killed thousands of fish across the country.
Mr Owen told the PA news agency: “Where I was this morning on a canal near Birmingham, fish were caught up against a lock and you saw hundreds of seagulls picking up the dead fish, the stench was really quite amazing.
“If July is like June, if August is like June, then we will get far more fish kills than we’ve ever seen. There is a knock-on effect.
“The fish are the visible bit because that’s what people see floating on the surface but it is also (about) what is happening to the ecosystem.”
In one case in West Yorkshire, people sat fishing have reported a stream of dead fish moving past.
Dr Andy Bray, catchment development manager at the Calder Rivers Trust, told PA: “We’ve got rivers that don’t have any shade, that are straight and that are impounded so there is very little flow. So it’s just kind of a backlog for them to just be heated up in.
“In some places, it’s like a steady stream ... of upturned fish floating down the river ... there are hundreds in a 30 or 40-minute period.
“This is a problem that’s going to be happening year on year as we go forward. Maybe not every year, but it’s going to be something that we’ll see again. You might even see again this summer.”
There was also an “unprecedented” number of fish deaths in June, according to John Ellis of the Canal and River Trust.
Mr Ellis told the BBC’s Today programme: “We’ve had more than 60 fish mortality incidents on 21 different canals up and down the UK and to put that into perspective, a typical year we may see half-a-dozen incidents.”
Mr Ellis told the BBC the increase in deaths was down to a combination of factors including high water temperatures and thunderstorms reducing the amount of oxygen in the water.
The Met Office also said the UK had had 68% of its average rainfall for June, with 52.2mm of rainfall.
Mark McCarthy, who works in the Met Office team responsible for weather and climate records, said: “It’s officially the hottest June on record for the UK, for mean temperature as well as average maximum and minimum temperature.
“June started with a good deal of high pressure and temperatures initially around average for many, but once that subsided, warm, humid air began to influence temperatures, with 32.2C the highest temperatures reached.
“What’s striking is the persistent warmth for much of the month, with temperatures widely into the mid-20s Celsius for many and even into the low 30s at times.”
