The nontuberculous mycobacterial group Mycobacterium avium-M. intracellular-M. scrofulaceum (MAIS) was isolated from 33% of the water samples collected from various aquatic environments in the southeastern United States. By contrast, only 20% of the water samples collected in the northeastern United States (New Jersey northward) yielded MAIS organisms. The most frequent recovery of MAIS organisms (37%) was from water samples with salinities from 0.1 to 1.9 g% (grams of NaCl/100 ml of sample). Other saprophytic slow- and rapid-growing nontuberculous mycobacteria were also isolated. The fewer MAIS organisms recovered from marine waters (20%) relative to those from freshwaters (37%) suggested that ocean water may not be a primary origin of these pathogens, although it still may be a source of infection. Our data implied a positive correlation between the frequency of persons reacting to MAIS antigens and the presence of these potential pathogens in the coastal region of the eastern United States.