The great river systems of the North American continent were the avenues by which the continent was explored. The search for a Northwest Passage was an attempt to find rivers or other water passages that would lead from the Atlantic Coast to the Pacific Ocean. The Northwest Passage was never found, although technically one exists when not frozen over by arctic ice. However, the rivers that rise on the eastern seaboard made it possible to push westward, a pioneering effort that eventually continued to the Pacific Ocean.

The Chesapeake Bay, the Hudson River, the St. Lawrence River, and others all played an important role in the trek West, but it was the mighty Mississippi-Missouri River with its route unhindered by falls that made possible the exploration of the continent as far as the Rocky Mountains. Canoes and sailing craft, pole boats and rafts, and other water-borne conveyances were the first means of transportation into the interior, and canal construction was essential in order to stabilize the water system, make it controllable during flood and drought, and remove the uncertainty from water navigation.

The Chesapeake Bay, which is entered by six major rivers (Susquehanna, Patuxent, Potomac, Rappahannock, York, and James) as well as many smaller rivers and estuaries, was the principal area of early settlement and the Potomac River, flowing from the hinterland near the Monongahela and Ohio River systems, became an important water route for the transportation of materials and people into and out of the heartland of the country. The escarpment of the Potomac River at Great Falls made it necessary to seek routes around the rapids, falls, and gorges and the Chesapeake and Ohio Canal had its beginnings in a company organized by George Washington, although the C&O was formally begun as such by John Quincy Adams. This combination of river and canal circumvented the falls and rapids and established a navigable route into the interior. Later, using water from the river, the C&O Canal was extended to Cumberland, Maryland, and the traveler was free of the vagaries of the river and the uncertainties of water levels. Thus, the movement of materials and supplies in and out of the interior of the continent became a fairly routine undertaking. Cumberland became an important transfer point where cargoes were trans-shipped into the Monongahela River system to be floated downstream to Pittsburgh and the Ohio Territory.

In the eastern United States the rivers that flow out of the Appalachian Mountains almost always cross a line of resistant rock that does not submit easily to erosion. As a result, most of the rivers flowing from the Appalachian Mountains to the Atlantic Ocean are studded with falls similar to the Great Falls of the Potomac. These falls made inland navigation extremely difficult, but water transportation was so essential to early settlers that is was considered worthwhile to construct canals bordering the rivers for safe, easy transportation routes.

The rivers and canals served as a means of transportation for many years, but in time the railroads proved to be a faster, cheaper way of moving goods over the vast distances and eventually they replaced most of the inland, waterborne commercial transportation. The Erie Canal and the Mohawk Canal in New York are among the few that have survived and that operate in modern commerce, but the C&O Canal was overwhelmed by the competition from the Baltimore and Ohio Railroad and went out of business. Now that the C&O Canal is being restored as a National Historical Park, it will represent an example of living history in a national recreation area ideally situated for convenient access by large numbers of urban dwellers. The operation of the locks and the movement of barges on the Canal will provide a vivid demonstration of our national heritage as well as outdoor recreation in a national park for nearby residents and visitors.

In an age of superhighways and jet planes, it is difficult to comprehend the enormous difference between the difficult and hazardous overland route through deciduous forests and the relative safety of the river system that brought the traveler to the same destination.

While the rivers functioned as the principal means of transportation, they also provided the basis for great adventures as Mark Twain's "Huckleberry Finn" testifies. In addition, the sternwheelers, the pleasure and excursion boats, and the showboats constituted a romantic and gallant way of life that many Americans look back on with nostalgia. With the advent of railroads, however, people shifted from water transportation to the new iron horse and, at the same time, the users of the rivers for industrial transportation and sewage disposal increased and brought about the decline of the river, a decline that with few exceptions continues to this day.