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Information was gathered on the distribution of white-clawed crayfish Austropotamobius pallipes complex in the watercourses of the Alessandria province (NW Italy), on the biological and ecological preferences of the species, and on the features of the biotopes in which it is found. A total of 409 sites on 361 watercourses connected to the main sub-basins of the Po River were analysed, with data gathered during the field research phase, conducted for three consecutive summers from 2002 through 2004. Thirteen percent of the sites investigated were found to currently house crayfish populations. The persistence in time of superficial water and natural morphology of the watercourse were found to be the chief requirements for the presence of crayfish. Data on land use, human density and other factors which potentially limit the survival of crayfish populations were also analysed.