Over 100 pesticides - including 24 that are not licensed for use in the EU - have been identified in Europe's rivers and canals, including the UK.
Twenty-nine waterways in ten European countries were tested in the study. All of them contained multiple pesticides, and most contained veterinary drugs.
The Greenpeace-led study, in collaboration with the University of Exeter, highlighted that the highest levels of contamination were found in a Belgian canal that contained 70 pesticides.
In 13 of the 29 waterways, concentrations of at least one pesticide exceeded European standards for acceptable levels.
“There is huge uncertainty about what effects these mixtures of chemicals could have on wildlife and human health,” said Dr Jorge Casado, who led the analytical work.
“We know many of these individual pesticides are a cause for concern.”
The researchers said the presence of unlicensed pesticides did not necessarily mean they had been used illegally, as they could have been used for other permitted purposes or before bans came into force or licenses expired.
However, they noted that several pesticides were found in multiple rivers, and said the concentration and frequency of carbendazim (found in 93% of samples) was “remarkable”.
The majority of the veterinary drugs detected were antimicrobials, most being antibiotics.
Dr Paul Johnston, who co-authored the paper, said: “This is not a case of us versus farmers or water companies.
“This is about using forensic scientific methods to investigate a problem that faces us all. We have to work together to find a holistic solution.
“Farmers don’t want to pollute rivers, and water companies don’t want to have to remove all that pollution again downstream, so we have to work to reduce reliance on pesticides and veterinary drugs through more sustainable agriculture.”
Of the 103 pesticides identified, almost half were herbicides and the rest were fungicides or insecticides.
The study took samples from waterways in Austria, Belgium, Germany, Denmark, France, Italy, the Netherlands, Poland, Spain and the UK.