Pittsburgh's three rivers have formed one of the key transportation systems throughout Western Pennsylvania and the Midwest for centuries. The first system of locks and dams were built in the mid-1800s as a way to improve navigation along these vital national arteries.

In 1893 the Army Corps of Engineers opened a permanent office in Pittsburgh with the mission of improving navigation on the Allegheny and Monongahela Rivers. Today, The Pittsburgh District system now includes twenty-three locks and dams along the Allegheny, Monongahela and Ohio Rivers. There are eight locks and dams on the seventy-two miles of the Allegheny River from the Point at Pittsburgh to East Brady, Pennsylvania, another nine locks and dams along the 128 miles of the Monongahela River from the Point to Faimont, West Virginia, and six more along the 127 miles of the Ohio River, from the Point to New Martinsville, West Virginia. They are all the responsibility of the Pittsburgh District engineers.

s The Monongahela River Locks and Dam #2 near the US Steel Edgar Thomson Works.

The three rivers that make up the Port of Pittsburgh are used to carry forty-one billion tons of raw materials, bulk and manufactured goods for many industries in the region. The Port of Pittsburgh is the second busiest inland port and the 17th busiest port of any kind in the nation.

The natural river beds consist of long, uneven downhill slopes with shallow areas and deep pools. The dams create an “aquatic staircase.” Each step on the slope of the riverbed is a pool of water extending miles upstream, maintaining sufficient depth for boats and barges. The normal flow of the river runs through these pools and the excess flows over the dam into the next pool and on down the river. The entire width of the river is not used for navigation, but there is a channel maintained at a nine foot depth for commercial vessels.

Each dam on a navigable river has at least one lock chamber to enable river traffic to go safely between pool levels. Vessels are lifted or lowered from one pool to the next inside the lock chamber. Raising or lowering from one pool level to the next is called a "lift." The lift of the locks in the Pittsburgh District ranges from 8 to 22 feet depending on the length of the pool. Pool length varies from as short as seven miles between locks up to forty-two miles.

The system of locks and dams have also done much to help control the seasonal flooding that for centuries plagued the cities along the three rivers. Although they can not prevent flooding, the system, along with a system of reservoirs, does provide some means to alleviate the potential for catastrophic flooding, such as the Great Flood of March 1936.

The Charleroi Locks and Dam along the Monongahela River.