A multinational research consortium has shown that cocaine metabolites in Swedish waters cause Atlantic salmon to travel farther, potentially disrupting ecosystems. The findings, published in Current Biology, highlight the first evidence of such effects in the wild. Cocaine and its metabolites have been detected increasingly in rivers and lakes worldwide, entering waterways primarily through wastewater treatment systems. Prior laboratory studies suggested behavioral changes, but this study confirms the phenomenon under natural conditions. The team, coordinated by Griffith University, the Swedish University of Agricultural Sciences, the Zoological Society of London, and the Max Planck Institute of Animal Behavior, implanted slow‑release devices into 105 juvenile Atlantic salmon in Lake Vättern, Sweden. The fish were divided into a control group, a group exposed to cocaine, and a group exposed to benzoylecgonine, the main metabolite commonly detected in wastewater. Over a two‑month monitoring period, salmon exposed to benzoylecgonine swam up to 1.9 times farther than controls, dispersing roughly 20 miles from the release point. "The location of the fish determines what they eat, what eats them, and how populations are structured," said coauthor Marcus Michelangeli. "If pollution is altering these patterns, it has the potential to affect ecosystems in ways we are only now beginning to understand." "The idea that cocaine might have effects on fish might seem surprising, but the reality is that wildlife is already exposed to a wide range of human-made drugs on a daily basis," added Michelangeli. A 2024 study by the Oswaldo Cruz Institute in Brazil showed that even sharks are exposed to cocaine, but little is known about its effects on animals in the wild. The current research expands that understanding to salmon and underscores the need to monitor metabolites, which are often more prevalent in waterways. Researchers plan to assess the prevalence of these behavioral changes across species, evaluate survival and reproductive impacts, and refine risk assessments to include metabolites.