Experts attributed the mass fish deaths in some rivers in the United Kingdom to climate change.
As the country battled for the hottest June ever recorded, authorities were alarmed as fish in rivers were seen floating ashore.
Robert Britton of Bournemouth University said in an interview with New Scientist that hotter temperatures reduce the amount of oxygen in the water.
Some cold-blooded fish, such as Atlantic salmon and brown trout, need highly oxygenated water to survive.
Reeked of sewage in UK river
Hot weather might be the most common contributor to fish deaths in the country; however, experts determined that sewage in rivers also leads to this phenomenon.
Professor Alistair Boxall and his team from the University of York collected water samples from the Foss River in Yorkshire in mid-June, as reported by The Press.
They also collected samples along the river at many locations, including Sheriff Hutton, Strensall, and New Earswick, as well as closer to the city center.
The samples revealed a high level of ammonia and nitrate, as well as extremely high levels of paracetamol (acetaminophen).
Boxall explained that the presence of paracetamol in rivers is an indicator that raw sewage is being thrown into the water because sewage treatment plants are normally highly adept at eliminating the drugs.
He added, paracetamol is unlikely to kill fish, but untreated sewage can significantly deoxygenate the river, resulting in mass fish deaths.
"The weather in the UK in recent weeks has been very dry and this led to a massive reduction in the [water flow] of the river Foss," he said. "And then there was this flash flood, which led to sewage systems being overwhelmed by rainwater, leading to the release of raw sewage into this river."
Boxall believed that climate change will cause additional mass fish death across the country.
Richard ffrench-Constant of the University of Exeter in the United Kingdom said climate change would result in greater sewage discharges into rivers due to periods of heavy rains.
The Environment Agency spokesperson said they are reviewing the information regarding the death of the fish in the river.
"The University of York has shared some data with us which we will be considering alongside findings from our own investigations, including the impact of recent hot weather on fish, to determine the probable causes of these issues," they added.
Read Also: Texas Fish Kill: Thousands of Dead Fish Along Coast Caused by Low Dissolved Oxygen
Report of death fish
As of this writing, the Environment Agency has received over 370 reports of dead fish, but this figure is expected to increase if the forecasted extreme weather persists.
"Environment Agency fisheries teams have been responding round the clock to numerous reports of dead or distressed fish across the country," said Dr. Graeme Storey, Fisheries Manager at the Environment Agency, as reported by Eco Magazine.
The agency also encourages the public to immediately report to the authorities any sightings of death fish or fish in distress.
Fish in distress appear lethargic or unresponsive, sometimes close to the bank, there is tight shoaling, and there is evident gasping at the surface. Stressed fish frequently exhibit signs of infection or fungus.
Related Article: Fish Kill in Louisiana Due to Lack of Oxygen, Experts Say Possible Uptick as Oceans Warm
Related Video: