Scientists have found what they called environmentally damaging levels of illegal drugs in the river running through Glastonbury festival owing to public urination on the site.

Researchers measured levels of illegal drugs in the river before, during and after the last Glastonbury festival, in 2019, comparing levels upstream and downstream of the event.

After the 2019 festival, drug levels in River Whitelake were high enough to harm aquatic wildlife, including a rare eel population, according to the report.

It found that the amount of MDMA was 104 times greater downstream than upstream in the weeks after the festival, rising to levels that could harm the life cycle of European eels, a protected species. Cocaine concentration was 40 times higher downstream, although the levels of cocaine were not considered harmful to aquatic life.

Previous research has shown that cocaine traces in rivers can cause eels to become hyperactive and experience muscle wastage, impaired gills and hormonal changes.

Dan Aberg, of Bangor University’s School of Natural Sciences, said: “Illicit drug contamination from public urination happens at every music festival. Unfortunately, Glastonbury festival’s close proximity to a river results in any drugs released by festival attendees having little time to degrade in the soil before entering the fragile freshwater ecosystem.”

A spokesperson for Glastonbury festival said that protecting streams and wildlife was of “paramount importance” to the festival and that they would be happy to work with the researchers to understand their results and recommendations.

“We have a thorough and successful waterways sampling regime in place during each festival, as agreed with the Environment Agency. There were no concerns raised by the Environment Agency following Glastonbury 2019.”

Ahead of that year’s festival, Glastonbury’s organisers launched a campaign, Don’t Pee on the Land, to raise awareness of the environmental damage caused by public urination on Worthy farm.

“Peeing on the land at Glastonbury causes pollution of the water table, which can affect local wildlife and fish,” they tweeted in June 2019. “The Environment Agency have the power to close the site if there is too much pollution. Please only pee in the hundreds of toilets and urinals on site.”

In response to the new research, Glastonbury’s spokesperson described public urination as “the biggest threat to our waterways and the wildlife for which they provide a habitat”.

They said the Don’t Pee on the Land campaign had had “measurable success” and that they would continue to discourage the practice. “We also do not condone the use of illegal drugs at Glastonbury,” they added.

The researchers monitored a nearby river, Redlake, which does not cross the festival site. It experienced “no significant changes in any illicit drug levels, further confirming that drug release was likely dependent on the festival site”.

They suggested further possible mitigation measures such as constructed treatment wetlands, also known as reed beds, which use natural functions, vegetation, soil and living organisms to provide additional treatment to wastewater.

Dr Christian Dunn at Bangor University called drug and pharmaceutical waste “a hidden, worryingly understudied yet potentially devastating pollutant”.

Glastonbury festival has been unable to take place since 2019 owing to the Covid-19 pandemic. Last week it put on sale accommodation packages for camper vans, tipis and pre-erected tents for 2022, suggesting a more hopeful outlook for next year’s festival.

In May, the organisers held a live stream, Live From Worthy Farm, featuring performances from acts such as Wolf Alice, Michael Kiwanuka and Coldplay.