Responsibility for operating, maintaining, and improving the waterway was assigned to the U.S. Army Corps of Engineers, Wilmington District. In the mid-1920s, work began to move the eastern entrance at Delaware City several miles south to Reedy Point, Delaware. All locks (except the one at Delaware City) were removed, and the waterway was converted to a sea-level operation at deep and wide. These improvements cost $10 million. Two stone jetties at the new eastern entrance were completed in 1926. The sole remaining lock at Delaware City — a stone structure, resting on wooden underpinnings, with a wooden floor — would eventually be preserved and, in 1975, listed on the National Register of Historic Places.