The introduction of non-native species is one of the main threats to biodiversity and freshwater ecosystems are extremely vulnerable to biological invasions. Procambarus clarkii and Pacifastacus leniusculus are problematic aquatic invasive species and are well known for their feeding plasticity. These species are capable of preying bivalves. In the last decades, freshwater bivalves have suffered major global declines, being the introduction of invasive species a possible important, but not well studied, threat. Given this perspective, the aim of this study was to assess the potential impacts of P. clarkii and P. leniusculus on freshwater bivalve populations. For this it was verified whether there is a predator-prey relationship between these crayfish species and native (Anodonta anatina, Potomida littoralis e Unio delphinus) and invasive (Corbicula fluminea) bivalve species through experiments in laboratory and sampling two rivers (Sabor and Maçãs) in the north of Portugal where all species live in sympatry. In the laboratory, crayfish feeding preferences in terms of bivalve species and competition between the two crayfish species were also assessed. In the field, abundances and length of the specimens of each bivalve species were recorded, crayfish predation marks on bivalves were quantified and crayfish distribution, abundance and sex were determined. All native bivalve species were preyed both in laboratory and in the field; however, P. clarkii and P. leniusculus were unable to prey the non-native C. fluminea. Bivalve predation was not affected neither by the lengths or sex of the crayfish. The most preyed native species by both crayfishes was A. anatina, while P. littoralis was the least preyed species. We also found competition for bivalves between the crayfishes, being P. clarkii the dominant species and displaying a more aggressive behaviour than P. leniusculus. In addition to direct mortality on native bivalves (which in the mesocosm experiments was extremely low) indirect effects can also be important (although not studied) because it is expected that animals with predation marks may have their fitness reduced causing impacts on bivalve populations and consequent effects on ecosystem functions and services (e.g. filtration, nutrient cycling, bioturbation). The results of this study support the idea that P. clarkii and P. leniusculus can affect native bivalves. These predators may have direct and indirect impacts on bivalve populations by reducing the number of effectives by increasing mortality and by reducing their fitness, which may have indirect impacts on freshwater ecosystems. On the other hand, the fact that these crayfishes do not prey C. fluminea offers this invasive bivalve another advantage over native species. Therefore, future management actions devoted to the conservation of freshwater bivalves should have in account the possible effects of invasive crayfishes on these organisms.