This chapter describes the procedures for measuring discharge in large streams by the moving-boat technique. During the traverse of a boat across a stream, a sonic sounder records the geometry of the cross section, and a continuously operating current meter senses the combined stream and boat velocities. These data are converted to discharge for the cross section quickly, efficiently, and inexpensively. Measurements obtained by the moving-boat technique compare within 5 percent of measurements obtained by conventional means. Field and office procedures applicable to this method are outlined. Theory of technique is developed and equipment required is described. Selection and preparation of the cross section is detailed. A complete facsimile example of computation of a moving-boat measurement is given, and the determination and application of adjustment factors are described.