Aquatic animals can maneuver and propel themselves through a variety of means, including the oscillation and undulation of flukes and fins. The motions of these can species develop thrust-producing, highly three-dimensional wakes. Experiments have shown that bio-inspired propulsors can operate with large propulsive efficiencies, with some efficiencies being greater than those of a screw-propeller propulsion system. In the current work, stereoscopic particle image velocimetry (SPIV) was used to characterize the wake produced by a rigid, bio-inspired trapezoidal pitching panel. Detailed analysis in terms of Strouhal number is the focus of the current work, and the Strouhal number range tested was from 0.17 to 0.56. The results show that a highly three-dimensional wake structure develops, which is composed of interconnected streamwise and spanwise vortex tubes. The streamwise vortex tubes induce spanwise flow toward the midspan that drives a spanwise compression of the wake. An increase in Strouhal number results in the movement of the location of wake breakdown upstream and more exaggerated spanwise compression of the wake.