Several environmental fate models have been developed that can be used for predicting concentrations of anthropogenic chemicals in the aqueous environment. Although individual models vary in their mathematical approach and the assumptions they are based on, all have in common basic premises concerning the factors controlling distribution and transformation of any chemical. The validity of the various assumptions made can best be tested by using the models to determine how well they predict observed concentrations of currently manufactured chemicals. In this paper, monitoring data for a surfactant, linear alkylbenzene sulfonate (LAS), are used to compare the utility and success of the exposure analysis modeling system (EXAMS), simplified lake stream analysis (SLSA), and fugacity models in predicting distribution and concentration within a single flowing stream. The results show that each model is most applicable at a particular stage in hazard assessment. Obtaining quantitative exposure predictions for generally released chemicals requires a better definition of the types of environments that will be encountered and a better understanding of the sediment-water interface.