Even familiar waterways are unpredictable, for if left untended, they grow dangerous again.
Waterways can’t be simply explored and mapped. They must also be marked, inspected, and continually maintained to ensure watercraft safety. River bottoms, shorelines, and harbors change continuously, sometimes from one day to the next—introducing a new danger where none existed before. Coastal and river travel are safe today largely because decades of vigilance and work. The U.S. Army Corps of Engineers, the U.S. Coast Guard, and its forerunner, the U.S. Lighthouse Service, have kept them so.