Fluid flows consistent with low-mode edge waves were evident in video observations of swash motions during a field experiment in which beach cusps developed on an initially smooth beach. As beach cusps grew, energy lying along low-mode dispersion curves increased. The most energetic edge-wave propagation direction changed from upcoast to downcoast as the orientation of the cusp horns rotated. These observations suggest a coupling between morphodynamics and hydrodynamics, and are evidence that beach cusp evolution might control low-mode edge wave dynamics.