This volume describes the development, application, and analysis of a methodology for forecasting probable effects of toxic chemicals on the production dynamics of a generalized aquatic ecosystem. It explains, in detail, how methods are derived for extrapolating the results of toxicity tests performed with laboratory populations, and it estimates the effects of toxins on corresponding populations in natural lakes and rivers. The methodology represents an innovative approach for using the vast amount of routinely collected toxicology data to forecast toxic effects. Furthermore, this book considers the implications of uncertainties associated with these extrapolations and attempts to directly consider them when making the forecasts. The results of the forecasts are then evaluated in the context of experiments performed in laboratory microcosms and larger outdoor ponds, where the effects of phenolic compounds were examined. Finally, are discussed the results in relation to modifying the aquatic system simulation mode, refining model parameter estimates, and modifying toxicity assays for collecting more ecologically relevant data. This book is unique in that it provides a working methodology to use when forecasting risk in probabilistic terms based on current toxicity test results. As a result, it will be an essential reference source for environmental scientists, aquatic ecologists, toxicologists, ecosystem modelers, and policy makers.