By following the rivers of the United States that empty into the Atlantic Ocean or the Gulf of Mexico, a boat can travel as far west as the Rocky Mountains, but no farther.
An imaginary line, called the Continental Divide, runs through the Rockies. All rivers on the east side of the Divide flow toward the Atlantic, toward the Gulf, or toward the Great Lakes. But all the rivers on the west side of the Divide flow toward the Pacific Ocean. So there’s no way for a boat to travel across America.
A boat can travel from New York to Chicago, though, by way of the Hudson River, the New York State Barge Canal (formerly called the Erie Canal), Lake Erie, Lake Huron, and Lake Michigan.
It’s also possible to travel by ship from New England to Florida without once entering the open seas. A system of rivers, bays, and canals, called the Intra-coastal Waterway, winds its way along the Atlantic Coast, and ships can use this inland waterway to avoid the rough waters of the ocean.
And another Intra-coastal Waterway leads ships from Florida all the way to Brownsville, Texas, on the Mexican border!