There’s an ‘invisible’ drug epidemic gripping the rivers of Britain.

Fish in innocent rural waters are being exposed to a wide array of illegal substances and it’s not clear what effect the chemicals are having on their bodies, scientists have revealed.

Researchers from King’s College London discovered cocaine in all the fish they tested in the UK as well as ketamine, pharmaceuticals and MDMA, the active ingredient in ecstasy.

It’s long been known that sinful city fish hoover up drugs, with the mighty Thames said to contain so much cocaine that it’s making the eels act very strangely.

But scientists didn’t expect to discover drugs in waterways outside the capital.

Undated handout photo issued by Emily Beament of The River Otter in Devon. Europe's rivers and canals contain more than 100 pesticides, including 24 that are currently banned, a study has found. PRESS ASSOCIATION Photo. Issue date: Monday April 8, 2019. Researchers tested samples from 29 waterways in 10 European countries, including two in the UK. See PA story SCIENCE Pesticides. Photo credit should read: Emily Beament/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.
This river might look beautiful, but it could be to fish who are loaded with drugs (Image: PA)
When scientists searched fish, the most common drug they found was cocaine (Image: Getty)

Dr Leon Barron from King’s College London added: ‘Such regular occurrence of illicit drugs in wildlife was surprising.

‘We might expect to see these in urban areas such as London, but not in smaller and more rural catchments.’

Before you go out to smoke or snort a fish, it’s worth remembering the level of drugs in each fish are too low to get you high.

However, we don’t what effects the drugs are having on water-dwellers.

Lead author, Dr Thomas Miller from King’s College London said: ‘Although concentrations were low, we were able to identify compounds that might be of concern to the environment and crucially, which might pose a risk to wildlife.

“As part of our ongoing work, we found that the most frequently detected compounds were illicit drugs, including cocaine and ketamine and a banned pesticide, fenuron. Although for many of these, the potential for any effect is likely to be low.’

A freshwater shrimp of the sort involved in the study (Image: Getty)  

During the study, scientists collected samples including the freshwater shrimp Gammarus pulex from five catchment areas and 15 different sites across the county of Suffolk

Professor Nic Bury from the University of Suffolk said: ‘Whether the presence of cocaine in aquatic animals is an issue for Suffolk, or more widespread an occurrence in the UK and abroad, awaits further research.

‘Environmental health has attracted much attention from the public due to challenges associated with climate change and microplastic pollution. However, the impact of “invisible” chemical pollution (such as drugs) on wildlife health needs more focus in the UK as policy can often be informed by studies such as these.’

Londoners are now racking up so many lines that eels in the Thames are becoming hyperactive – with the drug’s effects making their annual migration up the Thames more ‘erratic’.

Earlier this year, tests showed high levels of the class A stimulant near the Houses of Parliament.

Researchers found that downpours can overwhelm waste systems and lead to cocaine from drug user’s urine entering the river.

Houses of parliament cocaine picture: Getty
Cocaine does not have a good effect on eels (Picture: Getty)
Houses of parliament cocaine picture: Getty
Fish don’t snort cocaine but ingest it from water containing traces of human waste (Image: Getty)

King’s College London researchers said, ‘Increases in caffeine, cocaine and benzoylecgonine were observed 24 hours after sewer overflow events.’

Previous research has shown that even low levels of the drug are enough to affect eels – and make eels so hyperactive they’re at risk of serious injury.

Anne Capaldo of the University of Naples Federico II in Italy studied endangered European eels – and found that tiny amounts affected them.

The researchers kept 150 eels in tanks, some with a low level of cocaine (just 20 nanograms per litre).

The eels in the tanks with cocaine swam noticeably faster, and when dissected 50 days later, they showed damage to their skeletal muscle, used for swimming.

The researchers wrote, ‘Their skeletal muscle showed evidence of serious injury, including muscle breakdown and swelling.

‘Even low environmental concentrations of cocaine cause severe damage to the morphology and physiology of the skeletal muscle of the silver eel, confirming the harmful impact of cocaine in the environment that potentially affects the survival of this species.’