Littoral invertebrates of Cochran Lake, Michigan were either highly "plant-associated," and found infrequently away from aquatic macrophytes, or "free-swimming" among the plants. Plant-associated taxa were distributed according to available surface area. Numbers of peripyhton and detritus feeders, chiefly chydorid Cladocera and chironomid midge larvae, were highly correlated with diatom density, whereas filter-feeding Cladocera attached to the plants (Sida, Simocephalus) were not. Cyclopoid copepods characteristic of the littoral during the day (Macrocyclops, Eucyclops, and Microcyclops) were also found primarily on aquatic plant surfaces. Abundances of the chydorid Cladocera increased slightly at ngiht, while other taxa showed little diurnal variation. Free-swimmming species in the littoral (Bosmina, Ceriodaphnia) sometimes formed large patches covering many square metres. Larger species (Mesocyclops, Diaptomus, Epischura) greatly increased the numbers and diversity of this community at night. Sida crystallina, a filter feeder typically attached to plant surfaces, nonetheless swims frequently and well if disturbed. Juveniles moved between substrates more frequently than adults, and were found nearer the surface. Sites for reattachment were located visually. Frequent and often extensive episodes of swimming, especially by juveniles, provided a plausible explanation for the high concentrations of Sida observed on isolated plants, particularly those on the margins of stands of aquatic vegetation.