The application of spectral analysis techniques to sanitary engineering stream and estuary studies is discussed from a practical operational viewpoint. Techniques of interpretation and the data requirements are emphasized rather than the mathematical basis and details of the technique. The usefulness of spectral analysis in analyzing records obtained from continuous, automatic monitoring stations is pointed out. Spectral analyses applied to tidal height records and dissolved oxygen records obtained in a field study of the Potomac Estuary are discussed. The discussion is limited to the application of individual power spectra computation to sanitary engineering investigations. (Author)