To ascertain if the copepod, Eurytemora affinis, a suspected detritivore, can utilize detritus or associated microorganisms as a food source, an index of food utilization was established as greatest reproduction, determined by number of egg sacs and eggs per sac. Feeding experiments were conducted using three concentrations of algae, three species of bacteria, and detritus synthesized from wild rice plants, Zizenia aquatica, and dried marsh plants. Both autoclaved and unautoclaved detritus caused more reproduction than starved copepods and less than copepods fed algae. The unautoclaved detritus caused better reproduction than autoclaved detritus. The Eurytemora readily ingested clay particles ranging from about 2 to 15 microns, but disperse suspensions of that material could not be maintained.