One hundred and sixty-one river sites throughout the Thames catchment area were surveyed during the summer of 1995 and a number of habitat features were recorded in order to identify relevant habitat variables for the water vole (Arvicola terrestris; Arvicolidae). In addition, the role of the American mink (Mustela vision; Mustelidae) in determining the present distribution of water voles in the Thames region was investigated. The data were analysed by using generalized linear models (GLM).

Water voles were found in places characterised by low banks, unmodified channels, vegetated bars, submerged vegetation and were tolerant of moderate levels of bank reinforcement. The presence of mink was the most important variable. The results suggest that the American mink is the main factor determining the current distribution of water voles in this area. Restoration and recreation of habitat for water voles are likely to be a powerful tool in the recovery of water vole populations. It is hypothesised that mink control will be necessary only while the water vole population is small; once the population starts to increase both species could co-exist provided that the habitat is suitable.