The distribution of 15 typical freshwater bacterial groups in 15 diverse lakes in northern Europe was investigated using reverse line blot hybridization. Statistical evaluation of the data in relation to the characteristics of the lakes showed that pH, temperature, and the theoretical hydrological retention time of the lakes were most strongly related to variations in the distribution of bacterial taxa. This suggests that pH and temperature are steering factors in the selection of taxa and supports the notion that communities in lakes with short water turnover times are influenced by the input of bacterial cells from the drainage areas. Within the beta subdivision of the Proteobacteria (Betaproteobacteria), as well as within the divisions Actinobacteria and Verrucomicrobia, different subgroups were associated differently with environmental variables.