Cocaine pollution from wastewater is changing the behavior of young Atlantic salmon in the wild, a new international study shows.
Researchers fitted 105 juvenile salmon reared in captivity with acoustic tracking tags and slow-release implants containing either cocaine, its main metabolite benzoylecgonine or a harmless control substance. They released the fish into Lake Vättern, Sweden’s second-largest lake, and tracked their movements for eight weeks.
The study, published April 20 in the journal Current Biology, found that salmon exposed to benzoylecgonine swam up to 1.9 times farther each week and dispersed as much as 12.3 kilometers farther from the release site than unexposed fish.
"Cocaine pollution alters the movement and space use of Atlantic salmon (Salmo salar) in a large natural lake" https://t.co/XdSl9fzsdx
— Cell Press (@CellPressNews) April 20, 2026
Michael G. Bertram, Jack A. Brand, & colleagues@currentbiology pic.twitter.com/qRqye2Z0Ua
Benzoylecgonine, the breakdown product routinely found at higher levels than cocaine in polluted waterways, produced a stronger effect than the parent drug itself. Lead researcher Jack Brand of the Swedish University of Agricultural Sciences said the results highlight how everyday human drug use can reach wildlife through treated and untreated sewage.
The extra activity could force the young salmon to burn energy they need for growth and later migrations. It may also push them into poorer habitats or increase encounters with predators at a critical life stage. Atlantic salmon already face pressure from climate change, habitat loss and other stressors, so scientists say this added behavioral change could affect survival and population health in rivers worldwide.
The experiment is the first to document these effects in a real natural lake rather than a laboratory setting. Cocaine and its metabolites enter waterways globally through human excretion and incomplete wastewater treatment.
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The extra activity could force the young salmon to burn energy they need for growth and later migrations.
The extra activity could force the young salmon to burn energy they need for growth and later migrations.
