Emily O'Rourke, a PhD student at Cardiff University and lead author of the study, told BBC News that otters were a "sentinel" species, revealing "widespread environmental pollution" of British fresh waters. The research backs up a recent Environmental Audit Committee report which showed there was a "chemical cocktail" of pollutants in rivers.
Dr Elizabeth Chadwick, principal investigator on a long-term monitoring scheme called the Otter Project, encouraged members of the public to continue reporting otters found dead.
"Our research was possible though the ongoing collection of otters found dead from across Britain. Our archive has samples from more 4,000 individuals collected since 1992; it is a unique and important resource for understanding this protected species, and for understanding environmental contamination and health," she said.
The findings have been published in the peer-reviewed journal Environmental Science & Technology.