The freshwater Asiatic clam Corbicula fluminea is one of the most successful introduced bivalves in the world and, due to its high invasiveness; it can also be a potential vector for diseases and parasites, including fungi. With the aim of filling the gap in knowledge of any mycological information regarding this clam, we report the first characterization of the fungal communities associated with three populations of C. fluminea collected from three tributaries of the Ticino River (Lombardy, Northern Italy). By means of a culturable mycological analysis, 110 specimens were investigated and 83.6% of them yielded the isolation of 13 fungal species. Differences in timing of fungal development, distribution of taxa in the basin, abundance and frequency of the fungal community were highlighted. Four species were occasional, with a frequency of less than 5%, while another five species showed a frequency of almost 20%, locally reaching 40%. In particular, we highlighted: a) the presence of various fungal flora associated to C.fluminea, sometimes with stable colonization; b) the isolation of Geotrichum candidum, shown to be site-specific in one tributary with high abundance and frequency, which is well known for its generic pathogenity and might be related to a valve erosion observed in the associated Asiatic clam population; c) the first report in water ecosystems of Chaetomium nigricolor, which stably colonizes the three investigated populations of the Asiatic clam. Our results are encouraging for the continuation of research on the ecological role of the fungal communities associated with aquatic organisms.