Measurements of river velocity obtained using fixed side-looking Acoustic Doppler Current Profilers are compared to those obtained using regular, vertically-oriented Acoustic Doppler Current Profilers during gauging transects. The results presented were obtained at two French study sites: the Saône river in Lyon, and the Isère river in Romans-sur-Isère. The Saône river was equipped with a 300-kHz horizontally-mounted ADCP, and the Isère river with multiple horizontal ADCPs operating at 300 kHz, 600 kHz, and 1200 kHz. At the Isère site, for mean velocities of ~0.7 to ~0.8 m/s, good agreement was obtained for velocities measured within 15 meters of the wall, but as the distance from the side-looking ADCP increased, its measured velocities were increasingly underestimated. A distinct trend towards velocity underestimation with decreasing signal amplitude was also observed. Velocity comparisons at the Saône study site were generally in good agreement with one another. However, for downstream velocities less than 40 cm/s, the horizontal ADCP tended to underestimate velocity.