Two species of Rhizophydium infesting Pediastrum sp. from Carp Lake, Cheboygan County, Michigan, were isolated and grown on an agar medium and on a variety of killed organisms for the purpose of conducting a developmental and morphological investigation. The results of the study showed that such characters as the shape and size of the zoospores, the shape of the sporangia, and the number of discharge pores were constant for each species on all substrata. However, two morphological features, namely sporangial size of both chytrids and the endobiotic part of one species, were not constant on all the nutrient materials. Furthermore, the two fungi did not occur on healthy actively growing organisms, indeed they infested substrata that were non-living or killed by boiling.