Large-scale, outdoor microcosms were used to study the fate of anthracene, a polycyclic aromatic hydrocarbon, in the aquatic environment. The study provides a data set for describing the disposition of anthracene in the water and aufwuchs of the microcosms for the purpose of comparison with existing laboratory information and as an aid in refining and validating EPA's Exposure Analysis Modeling System and other computer models. Such models are used to estimate the exposure, fate, and persistence of synthetic organic chemicals in natural waters using easily measured physical and chemical properties of the compounds and the ecosystems. The major loss of anthracene from the channel was due to photolysis, with some loss attributable to volatilization.