The influence of nonlinear advection on estuarine exchange flow was investigated with observations at the transition between the James River and Chesapeake Bay, Hampton Roads, Virginia. Data were collected under different tidal forcing, wind forcing, and river discharge in 2004 and 2005. The relative contribution of nonlinear advective terms to the along-channel momentum balance had the same order of magnitude as pressure gradient and friction, verifying recent analytical and numerical model results. Both the magnitude and the spatial distribution of nonlinear advection showed fortnightly variability. Nonlinear advection was more influential on along-channel flow at spring tides than at neap tides because of increased tidal velocities, in a cross-sectionally averaged sense. The flow structures induced by each nonlinear advective process were investigated for the first time with observations. The lateral advection term vu(y). was found to enhance laterally sheared exchange acting along with Coriolis forcing at spring tides and opposing it at neap tides. Vertical advection wit,. showed similar spatial distribution as vuy, at spring tides but was vertically sheared (landward at middepth and seaward in the rest of the water column) at neaps. Longitudinal advection uu(x) augmented landward flow in the channel.