Aims: To determine the effects of single-species bacterial films and their associated extracellular products on the reattachment of young adult zebra mussels. Materials and Results: Ten strains of bacteria were isolated from surfaces where adult zebra mussels can be found attached in nature. Single-species biofilms were developed on both glass and polystyrene using these bacteria. The reattachment of zebra mussels (i.e. with byssal threads) was compared between surfaces with and without films. Although no differences were observed in mussel reattachment between glass surfaces with and without films ( P > 0.05, ANOVA ANOVA), a reduction in mussel reattachment between polystyrene surfaces with and without films was observed for seven of the 10 strains ( P less than or equal to 0.05 to < 0.001, ANOVA ANOVA). Bacterial extracellular products (BEP) were isolated from five bacterial films and tested for their effects on mussel reattachment. Four of the five sets of isolated extracellular products evoked the same effects as their respective intact biofilms. Conclusions: We conclude that depending on the substratum, individual strains of bacteria in biofilms can inhibit the reattachment of adult zebra mussels. In some cases, BEP were the source of the inhibitory effects. Significance and Impact of the Study: The nature of the substratum on which the biofilms develop affects properties of the biofilm and its extracellular components, which subsequently influences zebra mussel reattachment.