In 1999, 4 species of cyprinid were surveyed for myxozoan parasites in a watershed in Algonquin Park, Canada; Kathlyn Lake, Broadwing Lake, and Lake Sasajewun were included. Eight species of Myxobolus were found that differed in their prevalence and distribution among the 3 lakes. The oligochaetes and environmental parameters, including sediment types and aquatic plants, of these 3 lakes were surveyed the following year. Oligochaetes belonging to 17 species were collected from the 3 lakes. The distribution patterns of the oligochaete fauna, with respect to the environmental variables, were examined using canonical correspondence analysis. Naidids were predominant in all 3 lakes, particularly in the pebbly and sandy sediment of Lake Sasajewun. The highest percentage of tubificids occurred in the detritus and muddy substrate of Broadwing Lake. These findings indicate that the prevalence of certain oligochaetes is congruent with the absence or presence of particular myxozoan species and that substrates and aquatic plants influence the distribution of certain oligochaete species.