Measurable multiplication and protein synthesis rates were observed for various environments approximating those conditions occurring in a cold mountain stream. An extract of river bottom sediments provided a better nutrient source for the organisms tested than did river water from sites above and below a sewage plant on two low nutrient control media. Concurrent field studies on the river, using dialysis sac-culture techniques, also showed periods of bacterial multiplication. These data suggest that the aquatic environment associated with a clear mountain stream not only can maintain populations of enteric bacteria but also can supply sufficient nutrients to initiate multiplication and de novo protein synthesis.