Nontuberculous mycobacteria (21 isolates), biochemically similar to those that are recovered from humans, were recovered from rainwater and from natural river waters and their aerosols in the area of Richmond, Virginia, USA. Field experiments confirmed the existence of a natural mechanism for the transfer of significant numbers of mycobacteria from water to air. Aerosolization of potentially pathogenic mycobacteria from waters of the southeastern USA may be a major pathway for human infection.