Field methods, data analyses, and calculation are presented exemplifying procedures for oceanic dispersion prediction as a tool for forecasting power plant effects on the coastal zone. Measurements were made of dye, drogues and temperatures near Pilgrim Station's discharge (Plymouth, Massachusetts), and of currents and other variables across Massachusetts Bay. Analysis of current data illustrates separation of tidal, wind-driven and inertial constituents and their significance for dispersion. Dye and temperature dispersion are compared with the currents study, and diffusion coefficients estimated. Current data from coastal sites (New Jersey and Massachusetts) are analyzed to determine field requirements for dispersion estimates. Methods to calculate expected precision of estimates based on brief current records are developed. Model calculations predicting dispersion based on observed ocean currents are described. Formulae are derived to estimate the spatial distribution of impact from a discharge. A numerical model to calculate discharge dispersion in more detail is discussed and used to study time variations of discharge effects. Model predictions are compared with field observations.