Otter populations crashed in Britain around the 1960s from the lethal effects of chemical pollution in rivers and lakes – or so we thought. Our research has looked more closely at what happened to otters in Britain over the last 800 years and has revealed a more complex picture.

Since Eurasian otters (Lutra lutra) are at the top of the aquatic food chain in Britain, any contamination consumed by their prey, and by the prey of their prey, accumulates in otters. So otters are particularly susceptible to any toxic chemicals in their environment.