A study on cocaine's effect on eels found that the creatures appeared hyperactive and sustained injuries to their skeletal muscles because of the drug

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London’s cocaine problem could become an eel problem.

According to Business Insider, high levels of the Class A drug have been detected in the water of the U.K. city’s Thames river.

The cocaine appears to have entered the river via water from London’s sewage systems that sometimes overflow into the Thames during periods of heavy rain. Cocaine initially enters the sewage systems through the urine of cocaine users.

A research team from King’s College London recently tested the water overflowing from London’s sewage systems into the Thames and detected levels of cocaine that are noticeably higher than those of other cities.

“Essentially everything in the water will be affected by drugs like these. A lot of the triggers and the ways that cocaine affects the system is really primal,” James Robson, a senior curator at the SEA LIFE London aquarium, told Business Insider.

For the numerous eels in the Thames — who, according to the Independent, recolonized the Thames Estuary “after it was considered ‘biologically dead’ in the 1960s” — this would likely mean “hyperactive” behavior.

In response to growing concern about the level of drugs in the Thames, a group of biologists at the University of Naples Federico II conducted an experiment with eels and cocaine-laced water in June 2018 and wrote up their results for the journal Science of the Total Environment.

For the study, the biologists left live European eels in water that had a small dose of cocaine, reportedly comparable to what is found in the Thames, reports The Independent. The eels in the cocaine water appeared more hyperactive to the biologists than the eels in cocaine-free water. The drug also caused serious injury to the eels’ skeletal muscle, which was slow to heal after the eels were removed from the water with the cocaine.

“This study shows that 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,” the 2018 report reads.

However, Robson told Business Insider that the eels in this study had more exposure to cocaine than the eels of the Thames, and that Thames eels are not likely being affected in the same way.

“You haven’t got a lot of disco-dancing fish down the bottom of the Thames,” he said.

The aquarium curator added that animal lovers and conservationists should be more concerned about the effects of plastics pollution and climate change on London’s sea life, since both of these threats are capable of doing far more damage to eels, fish and other animals than cocaine.