The Ohio River

The Ohio River forms where the Allegheny and Monongahela rivers meet at Pittsburgh and runs about 981 miles (1,579 km) southwest to join the Mississippi at Cairo, Illinois. Though shorter than the Mississippi or Missouri, it carries more water than either where it reaches the great river — it is the Mississippi system's largest tributary by volume. For much of its length it forms the border between the Midwest and the South.

The river was the gateway to the early American West, floating settlers and flatboats down into the Ohio Valley and serving as a dividing line between free and slave states before the Civil War. Today a series of locks and dams keeps it navigable year-round, and it remains a heavily used commercial waterway, lined with industry and carrying coal, steel, and chemicals between the Appalachian interior and the Mississippi.

• Pittsburgh
  The Steel City, where three rivers meet begins at
• Louisville
  A river city at the Falls of the Ohio flows through
• The Mississippi River
  The great river that drains the American heartland tributary of