Three species of freshwater sponges (Porifera): Spongilla lacustris (Linneaus), Eunapius fragilis (Leidy) and Ephydatia muelleri (Lieberkuhn) were identified in four southern Lake Michigan harbors: Belmont (IL), East Chicago (IN), Michigan City (IN) and St. Joseph (MI). Samples were collected from artificial substrates and are the first report of sponges in three of the harbors. Sponge cover on revetment walls, stone rip-rap and wood pier posts ranged up to 13% of the available surface area, whereas no sponges were growing on the soft silt bottom. Eunapius fragilis appeared to be the most common species. An angle-density relationship was observed for sponges growing on the stone rip-rap in Michigan City and East Chicago; as the orientation of the attachment substrate changed from horizontal to vertical, the density of sponges increased.