Stephen Wilson, age 11, of Providence, R.I., for his question:

HOW LONG IS THE ATLANTIC INTRACOSTAL WATERWAY?

A sheltered water route used by boats along the Atlantic Coast of the United States is called the Atlantic Intracostal Waterway. The waterway is 1,200 miles long, extending from Boston, Mass., to Miami, Fla.

A series of rivers, estuaries, inland bays, sounds and inlets, nearly all linked by canals, make up the waterway. United States Army engineers are continually dredging it. Its channel has a depth of 12 feet or more.

Barges and small pleasure boats use the waterway. They are exposed to the open ocean for only about 50 miles south from Boston, along the Rhode Island coast and for a 37 mile stretch along the New Jersey coast.

A canal extends from Philadelphia to Chesapeake Bay. The reminder of the waterway lies back from the shoreline, or is protected by islands and sand bars.

About 175 bridges cross the waterway. Twenty two lighthouses help guide the ships. Water locks lift and lower boats to different levels in the Dismal Swamp Canal in eastern Virginia and in eastern North Carolina.