York: River Foss paracetamol level is 'evidence of sewage'

And they claim the new figures are "clear cut" evidence that there was sewage present in the River Foss at the time several fish were found dead.

The fresh evidence has now promted the Environment Agency to review the findings of its investigation into the death of fish in the York river last month. 

Following tests on the river on June 20, the scientists from the University of York said they found concentrations of the medicine paracetamol among the highest ever reported in any river in the world.

Dr John Wilkinson, from the department of environment and geography at the university, said the findings show "undeniable" evidence of sewage in the river at the time.

Dr Wilkinson said: "The most clear cut evidence of a sewage overflow on June 20 are the concentrations of paracetamol in the river.

"Paracetamol is a good indicator of untreated sewage as wastewater treatment plants are very effective at removing it from sewage. Hence, a high concentration of paracetamol in a river is a strong indication that untreated sewage is likely present."

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Dr Wilkinson said the team had been studying pharmaceuticals in the Foss for years and, for context, the median paracetamol concentration across a recent year-long study in the river, covering 60 samples, was 40.8ng/L (nanograms per litre).

He said that in the sample collected at New Earswick footbridge on June 20 the team found 90,200ng/L of paracetamol.

"This is by far the highest concentration of this chemical we've measured in the Foss over the seven years we've been studying the river," he added.

"What this tells us is that we're confident untreated sewage was discharged into the Foss on June 20 between Strensall and Earswick."

The Environment Agency (EA) previously said the fish deaths were caused by a combination of high temperatures and thunderstorms creating a lack of oxygen in the river for the fish.

Several dead fish were spotted in the Foss in June (Image: Howard Jones)

But, following the findings from the university, the EA said it is reviewing the data.

An EA spokesperson said: “We are reviewing information surrounding the recent deaths of fish in the River Foss.

“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.”

The EA said its fisheries teams have been responding round the clock to numerous reports of dead or distressed fish across the country.

"During the month of June, we responded to 132 reports of fish kills across Yorkshire, compared to six reports in May," the spokesperson added.

Yorkshire Water said it has supported the EA's investigation into the fish deaths in York - and they remain confident that the incident is related to warm temperatures and low dissolved oxygen in the water.

"We are not being investigated in relation to this incident," a spokesperson said.