Few studies have examined community structure among myxozoan species in fish. Herein myxozoan communities are described from 2 cyprinid species, the spottail shiner (Notropis hudsonius) and the common shiner (Luxilus cornutus), from mesotrophic and eutrophic localities in rivers in southwestern Quebec, Canada. Four myxozoan species were found, and total prevalence ranged from 60 to 86.7% in spottail shiners at 4 localities along the Richelieu River. Component species richness ranged from 2 to 4 and mean infracommunity richness from 0.87 to 1.47. Prevalence, component species richness, and infracommunity species richness in the spottail shiner were comparable to those from other localities in the Great Lakes and St. Lawrence River that were exposed to municipal effluents. Nine myxozoan species were found in common shiners from the Bras d'Henri micro-watershed. Component species richness varied from 6 to 8 at 4 localities, with total prevalence being 100% at all localities except 1, where it was 80%. Mean infracommunity richness ranged from 1.73 to 2.27. Prevalence, component species richness, and infracommunity species richness in the common shiner from the Bras d'Henri micro-watershed were among the highest observed for myxozoan communities from any host species to date. It is concluded that moderate levels of eutrophication are sufficient to generate species-rich communities of myxozoan parasites in fishes.