Trout are becoming hooked on drugs dumped in the sea.
Trout are getting addicted to drugs
Substances ranging from anti-depressants to cocaine are seeping into streams and rivers and are leaving stoned trout without fear of their predators.
Michael Bertram, from the Swedish University of Agricultural Sciences, said: "There are a few pathways for chemicals to enter the environment. Inadequate treatment of pharmaceuticals during production is one way. Another is during use.
"When a human takes a pill, not all of that is broken down in bodies so through our excrement, the effluent is released into the environment."
Experts have called on pharmaceutical firms to make drugs that won't break down and harm wildlife.
Gorka Orive, at the University of the Basque Country, said: "Drugs must be designed to not only be effective and safe, but also to have a reduced potential risk to wildlife."