The disappearance rate of 2,6-dichlorophenol in a small stream was studied and showed to be first order with respect to either distance or time of flow. Average half-life in the stream was about 4 hours. It is suggested that the disappearance was due to degradation within the biofilm covering the stream bed and that the rate is controlled by diffusion of 2,6-dichlorophenol across the water biofilm interface.