Water samples removed from two rivers and from the subtidal zone of Georgia Strait in British Columbia were treated with either 0.025 ppm of DDT, lindane, α-chlordane, or γ-chlordane, or 0.1 ppm Aroclor 1260 (PCB). The samples were incubated in the laboratory for up to 12 weeks at the temperatures of these natural waters at the time of sampling. Lindane persisted in all water samples throughout the experiment, but large proportions of the other compounds were transported into the atmosphere during incubation except when the containers were sealed. No metabolic breakdown could be demonstrated. As demonstrated with 14C-γ-chlordane, uneven distribution of the pesticides occurred rapidly, but was prevented, or reversed, by addition of a surfactant to the water. Total bacterial counts were generally higher in treated than in untreated water samples.