Biofilms of a municipal water distribution system were characterized to assess the occurrence of fungi within surface matrixes. Densities of filamentous fungi ranged from 4.0 to 25.2 CFU cm(-2), whereas yeast densities ranged from 0 to 8.9 CFU cm(-2). Observations by scanning electron microscopy further suggested that spores, not hyphae or vegetative cells, comprised the primary source of viable propagules.