Circular corrugated pipes are used as culverts at road crossings, and in many regions in Canada, the United States, and other countries, they have to be designed to allow fish passage during periods of fish migration. In many of these culverts, if the velocities are too large to allow fish passage, some type of baffles need to be installed to reduce the velocities. This paper presents the results of a laboratory study of the velocity field in turbulent open-channel flow in a circular corrugated pipe of diameter 0.622 m for three slopes of 0.55%, 1.14%, and 2.55% and a range of discharges from 30 l/s to 200 l/s. The Manning n was found to be equal to 0.023. Velocities were relatively small in some portion of the flow near the boundary of the pipe, and these low velocity regions may be useful for fish passage upstream. In the region of fully developed flow, in the central vertical plane, the longitudinal velocity was described by the Prandtl equation for rough turbulent flow, with a dip in the velocity profiles near the water surface. The velocity profiles in the noncentral planes were also described by the Prandtl equation for rough turbulent flow, but with a significant dip in the upper part of the flow. An empirical method was devised to describe the geometrical and kinematical properties of this velocity dip. The general findings of this study were also found to be valid for flow in a large corrugated pipe of diameter of 4.27 m with two slopes of 0.14% and 1.42%.