Delaware Bay, entrance bet. Cape Henlopen, Del. (SW), and Cape May, N.J. (NE), is 12 mi/19 km wide; bay expands to 25 mi/40 km just inside entrance, tapers to c.7 mi/11.3 km to NW to become Delaware R. estuary. Intracoastal Waterway traverses length of bay, from Chesapeake and Delaware Canal, which enters Delaware R. from W, to canal crossing Cape May.