00:58 Britain’s Rivers So Polluted, Endangered Eels are Getting High A new study finds rivers in Britain are so polluted, critically endangered eels are getting high.

At a Glance Researchers found that trace amounts of cocaine can cause hyperactivity and weakened muscles in eels.

Eels were subjected to the amount of cocaine that has been found in European rivers and water systems.

Traces of cocaine flushed into rivers is harming endangered European eels, a new study says.

Researchers for the study published in the Science of the Total Environment say minute amounts of cocaine , which is one of the most abundant illicit drugs found in surface waters, is sufficient to alter the physiology of European eels, enough so that it may hinder their long migrations through the oceans to reproduce.

The scientists subjecting laboratory eels to 20 billionths of a gram of cocaine per liter of water for 50 days, which is the equivalent amount of cocaine from illicit drug use that has been found in European rivers and water systems.

The eels subjected to the cocaine became hyperactive and their muscles showed evidence of serious injury, including breakdown and swelling, researchers said.

The eels were then detoxed in clean water for 10 days, but the detrimental effects to muscles continued and appeared to be permanent.

"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,” lead author Anna Capaldo of the University of Naples Federico II wrote in the study.

The researchers also noted an increase in the stress hormone, cortisol, which can decrease the fat in the fish needed for long migratory journeys, and increased levels of dopamine, which could stop them from reaching sexual maturity.

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The researchers determined the amount of cocaine to use on the eels based on several previous studies tracking the amount of cocaine in European rivers , including cocaine found in the Thames near London's Houses of Parliament and in several Italian rivers.

European eels spend 15 to 20 years in European rivers before embarking on an up to 3,700-mile trek across the Atlantic Ocean to spawn in the Sargasso Sea and along the U.S. Eastern Seaboard, according to National Geographic.

Overfishing, water pollution and development have had a significant impact on silver eel populations, prompting the International Union for Conservation for Nature to declare them critically endangered .

Capaldo said further study is needed to examine how the eels' muscle damage from cocaine impacts the species' long migration and reproduction.