The outfalls of the eight tributaries entering Grand Lake-St. Marys were monitored during the eleven month period from August, 1972 through June, 1973. Both biological and physical parameters were measured at all sites.The biological parameters that were measured included; fecal coliforms, fecal streptococci, Salmonella spp., Shigella spp., Proteus spp., seudomonas,aeruginosa and Staphylococcus aureus. The physical parameters were; pH, turbidity, water temperature, dissolved oxygen and local rainfall.All eight outfalls were shown to exceed the limits recommended by the U.S. Public Health Service for fecal coliform counts. The ratio of fecal coliforms to fecal streptococci suggested that the pollution came from both human and animal wastes that were carried into the lake in stormwater runoff. The low fecal counts obtained away from the tributaries, in the center of the lake, indicated that the lake was able to recover from the pollution entering at the outfalls. Primary contact recreation in the vicinity of the tributary outfalls is not recommended but the remainder of the lake presents no apparent health hazard.Ball State UniversityMuncie, IN 47306