Variations in the depth distribution and size of operculate and pulmonate gastropod populations were studied in Douglas Lake, Michigan. The species studied, in order of decreasing abundance, were: Helisoma campanulata, Campeloma decisum, Goniobasis livescens, H. anceps, Lymnaea catascopium, Physa integra, and P. parkeri. Peak densities occurred at 0.5 m for G. livescens, 3 m for C. decisum, 6 m for H. campanulata, H. anceps, L. catascopium, and P. integra, and 9 m for P. parkeri. Helisoma campanulata were found at greater depths as water temperatures rose. Decreases in population size occurred for H. anceps, L. catascopium, P. integra, and P. parkeri while an increase occurred for C. decisum.