This study analyses the composition, species richness and diversity (H') of aquatic molluscan communitiesin temporary water bodies within the valley of the lower Bug River in eastern Poland. The investigations were carried out in 2007–2009 within the section of the valley located between 190th and 50th km of the river course in 50 water bodies. Relatively rich and diverse malacofauna was found in the investigated habitats: 32 snail species and 6 bivalve species. Species diversity (H') in individual water bodies ranged from 0.44 to 3.48. About 40% of all mollusc species showed frequencies of 10%. Dominance patterns varied much among the water bodies. Mollusc abundance ranged from 20 to over 1,800 indiv./m2. Considerable species richness and diversity were found both within the active floodplain and the former one. This was probably related to the long duration of many of the investigated water bodies, as well as their periodical hydrological connectivity with permanent ones or river channel. From 9 to 12 samples should be enough to compile representative specieslist of molluscs inhabitingtemporary water bodies, but as many as 28–40 samples would be necessary to obtaincomplete dataset.