The Chesapeake and Delaware Canal is a man-made waterway connecting the head of the Chesapeake Bay and the upper reaches of the Delaware estuary. We found significant subtidal variability along the canal during a 1-month survey in 1975. There were significant differences between subtidal sea level fluctuations at the two ends of the canal, reflecting the different response characteristics of the two adjoining estuaries to atmospheric forcing. The resulting hydraulic head along the canal forced energetic subtidal volume flux through the canal which was of the same order of magnitude as the Delaware River discharge during the spring freshet period. ¿American Geophysical Union 1987