Salmon exposed to cocaine in the water swim longer distances than those that go without, according to a study released this week.
Cocaine use is on the rise worldwide, with the U.N. reporting an estimated 25 million people used the stimulant in 2023 and the drug being increasingly found in waterways.
Joint research released Monday by scientists at Australia’s Griffith University and the Swedish University of Agricultural Sciences studied how the drug affected the movements of wild fish in their natural habitats.
Researchers took 105 wild Atlantic salmon in Sweden’s Lake Vattern and exposed them to both cocaine and benzoylecgonine — a metabolite created by the drug in the liver — and then tracked their movements.
They found the river-dwellers exposed to the drugs traveled 1.9 times farther per week than their clean-living control cousins.
Those exposed to the by-product also swam 7.6 miles farther, the study found.
“Any unnatural change in animal behavior is a concern,” report co-author Marcus Michelangeli from Griffith University’s Australian Rivers Institute told national broadcaster ABC.
“We’re finding higher and higher concentrations of not just illicit drugs but all types of pharmaceuticals in our waterways.”
Researchers have warned the pollution of waters by common drugs poses “a major and escalating risk to biodiversity.”
“The idea of cocaine affecting fish might seem surprising, but the reality is that wildlife is already being exposed to a wide range of human-derived drugs every day,” Michelangeli said. “The unusual part is not the experiment, it’s what’s already happening in our waterways.”
Associate professor Michael Bertram at the Swedish University of Agricultural Sciences said the study showed the need for improving wastewater treatment and monitoring.
“Our study shows that drugs are not only a societal issue, but also a concrete environmental challenge,” he said.
A separate study released last month found that sharks in the Bahamas are consuming substances including caffeine, painkillers and cocaine.
“While the detection of cocaine — an illicit substance — tends to draw immediate attention, the widespread presence of caffeine and pharmaceuticals in the blood of many analyzed sharks is equally alarming,” lead author Natascha Wosnick told CBS News. “These are legal substances, routinely consumed and often overlooked, yet their environmental footprint is clearly detectable.”
In another study from 2024, scientists reported that sharks in the waters off Brazil tested positive for cocaine and benzoylecgonine.