Estimating the response of a river or stream to any proposed pollution abatement action is one of the most complex problems facing the sanitary engineer. In this work, recently developed modeling and forecasting techniques such as invariant imbedding, optimal and nonlinear filtering, and time series analysis are applied to the modeling, estimation, and forecasting of stochastic water quality streams. It is shown that these schemes and models will enable community planners to improve their planning, design, and operation of waste treatment and water supply and demand problems. In Volume I, the modeling and forecasting of stream quality by time series analysis and spectral estimation are discussed.