The Atlantic Intracoastal Waterway serves ports from Boston to Key West, Fla. The route is linked by several essential man-made canals, including the Cape Cod, Chesapeake and Delaware, and Chesapeake-Albemarle. The lowest controlling depth is 6.1 feet (1.9 m) in the Dismal Swamp Canal of Virginia and North Carolina. During World War II, the route became important as a means of avoiding the submarine menace along the coast. Commercial traffic (oceangoing vessels and barges) serves the heavily concentrated industrial areas north of Norfolk, Va; whereas, to the south, the waterway accommodates mainly pleasure craft traveling to the Florida resort areas.

The Gulf Intracoastal Waterway serves ports for more than 1,100 miles (1,800 km) between Brownsville, Texas, and Apalachee Bay, Fla. It lies mainly behind barrier beaches and provides a 150-foot-wide, 12-foot-deep channel. At its eastern end, the waterway is not directly connected with its Atlantic counterpart, except via the open waters of the Gulf of Mexico and the 6-foot-deep Okeechobee Waterway in southern Florida. The heaviest commercial activity is centred at New Orleans and extends eastward to the Black Warrior–Tombigbee river system at Mobile Bay, Ala., and westward to the major Texas ports. The Plaquemine–Morgan City Waterway provides direct connection west of New Orleans with the extensive Mississippi River valley system of inland waterways, and the Harvey Lock at New Orleans furnishes a direct entrance to the Mississippi River. Part of the Gulf route at New Orleans consists of the Inner Harbor Navigation Canal, an artificial waterway that is the axis of a major industrial district. Among the principal items moved on the route are petroleum and its products, industrial chemicals, pipe and other supplies for the oil fields, and sulfur.