The Monongahela River ( , ), sometimes referred to locally as the Mon (), is a river on the Allegheny Plateau in north-central West Virginia and Southwestern Pennsylvania. The river flows from the confluence of its west and east forks in north-central West Virginia northeasterly into southwestern Pennsylvania, then northerly to Pittsburgh and its confluence with the Allegheny River to form the Ohio River. The river includes a series of locks and dams that makes it navigable.
Etymology
The Unami word Monongahela means "falling banks", in reference to the geological instability of the river's banks. Moravian missionary David Zeisberger (1721–1808) gave this account of the naming: "In the Indian tongue the name of this river was Mechmenawungihilla (alternatively spelled Menawngihella), which signifies a high bank, which is ever washed out and therefore collapses."
The Lenape Language Project renders the word as Mënaonkihëla (pronounced ), translated "where banks cave in or erode", from the verbs mënaonkihële "the dirt caves off" (such as the bank of a river or creek, or in a landslide) and mënaonke (pronounced ), "it has a loose bank" (where one might fall in).
Monongalia County and the town of Monongah, both in West Virginia, are named for the river, as is the city of Monongahela in Pennsylvania. (The name "Monongalia" may be a misspelling that resulted from Monongahela being spelled wrong when the county was originally founded.)
Variant names
The USGS name for the river is the Monongahela River; there have been numerous alternative names, alternative spellings and misspellings in historical texts.