The Eurasian otter (Lutra lutra) is recovering from well-documented population declines that occurred during the 20th century. Little is known about the genetic impact of these declines in northern Britain and the current understanding of otter genetic structure in Britain is incomplete. This study reexamines genetic structure in Scotland, one of the otter's major strongholds in the United Kingdom, and combines data with a published microsatellite data set from the remainder of the United Kingdom to produce the 1st comprehensive assessment of genetic structure across the entirety of mainland Britain. We show that there is a remarkable contrast in genetic structure of otters in northern Britain compared to the south. Population fragmentation and high levels of genetic structure were typical of southern Britain, whereas in the north we observed a virtually panmictic population. These results imply very different demographic histories of otters in these 2 regions. Our findings also suggest a more favorable environment for the Eurasian otter in recent times in the north of the United Kingdom, possibly linked to human population density and anthropogenic habitat impacts. This study therefore provides a complete description of population genetics of the Eurasian otter in the United Kingdom, and allows inferences to be made regarding the relative importance of landscape characteristics on the recovery of otter populations.