Assemblages of freshwater gastropods were studied in nine pools within the largest wetland fringing a lake (Lake Neuchâtel) in Switzerland, i) to assess the relative importance of three spatial levels of differentiation (between two geographic sectors, between pools, and between habitats, i. e. helophyte vs. hydrophyte stands), and ii) to specify their habitat requirements. Relationships between species composition of gastropod assemblages and environmental variables (water and sediment characteristics) were assessed at the between-pool level. With 18 aquatic gastropod species recorded, the present study, although relatively limited in its scope (70 individual samples taken once), encompassed nearly 70% of the gastropod species available in this wetland and half of those of Switzerland. Significant differences were observed at all three spatial levels considered, in terms of species richness and individual species abundances. However, the habitat level seemed to be a major source of heterogeneity in the assemblages. Helophyte stands had denser and richer gastropod assemblages. Ordination and classification of the environmental and gastropod data revealed a good correlation between these two sets and allowed the setting up of a typology of species associations and their environmental requirements.