Wild Atlantic salmon exposed to cocaine and its metabolites are swimming significantly farther than normal, according to a groundbreaking study conducted in Sweden’s Lake Vättern. Researchers found that fish administered benzoylecgonine—a chemical produced when the body breaks down cocaine—swam up to 1.9 times farther each week than unexposed salmon, with some individuals traveling as much as 12.3 kilometers (7.6 miles) more over the eight-week tracking period.
The study, published in the journal Current Biology, marks the first time scientists have investigated the impact of cocaine pollution on fish behavior in a natural environment rather than a laboratory setting. Over the course of two months, 105 young Atlantic salmon were divided into three groups: one received cocaine, another received benzoylecgonine, and a control group remained untreated. All fish were implanted with tracking devices before being released into Lake Vättern, Sweden’s second-largest lake.
Scientists observed that while cocaine exposure did not shorten the salmon’s lifespan, it dramatically altered their movement patterns. The exposed fish exhibited heightened swimming activity, suggesting the drug interferes with their natural behaviors related to feeding, predator avoidance, and migration.
“Where a fish goes determines what it eats, what eats it, and how populations are structured,” said Marcus Michelangeli, a co-author of the study from Griffith University’s Australian Rivers Institute. “If pollution is changing these patterns, it could affect ecosystems in ways we’re only beginning to understand.”
The findings highlight growing concerns about pharmaceutical and illicit drug pollution in freshwater systems worldwide. Cocaine and its metabolites enter waterways primarily through human wastewater, as the body excretes traces of the drug via urine. Many wastewater treatment plants are not designed to fully remove these complex chemical compounds, allowing them to persist in rivers, lakes, and estuaries.
Traces of cocaine and benzoylecgonine have already been detected in waterways across Europe, including in Spain, Germany, and the United Kingdom. As usage remains high globally, scientists warn that even low-level contamination may disrupt aquatic wildlife in subtle but significant ways.
This research adds to a growing body of evidence that human drug consumption has far-reaching environmental consequences—not just for public health, but for the behavior and survival of wildlife in shared ecosystems.
