119 brackish water habitats up tidal stretches of rivers and along a 220 km strip of coastline in East Anglia were searched for Hydrobia ventrosa (Montagu) and H. neglecta Muus. The presence of H. ulvae (Pennant) and Potamopyrgus jenkinsi (Smith) was also recorded. The number of sites containing H. ulvae was 47, P. jenkinsi 32, H. ventrosa 25 and H. neglecta 11. This represents an approximately four fold increase in known sites for the last two species in the British Isles. The salinities of sites recorded for the Hydrobia species overlap considerably. All four species may be found in non-tidal brackish dykes and lagoons. However H. ventrosa and H. neglecta show a strong preference for shallow nontidal waterbodies, whereas H. ulvae is closely associated with tidal habitats. P.jenkinsi, in this study, exhibited a preference for nontidal dykes of low salinity.