Мононгахела өзені: АҚШ-тың Пенсильвания және Батыс Вирджиния штатындағы су жолы

River in Pennsylvania and West Virginia, United States

The Monongahela River (/m//ə/,/n//ɒ//ŋ//ɡ//ə/'/h//iː//l//ə/ məNONGgəHEElə, / /'/h//eɪ// / HAY ), sometimes referred to locally as the Mon (/m//ɒ//n/), is a 130 mile (209 km) 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.

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" is either a Latinized adaptation of "Monongahela" or simply a variant spelling.)

The USGS name for the river is the Monongahela River; there have been numerous alternate names, alternate spellings and misspellings in historical texts. efn|including Malangueulé, Me nan gi hil li, Meh non au au ge hel al, Mehmannaunringgehlau, Mehmannauwinggehla, Mo hon ga ly, Mo hon galy, Mo hon gey e la, Mo hong gey e la, Mohungahala, Mohunghala, Monaung, Monaungahela, Monna, Monnyahela, Monona, Mononga, Monongahalia, Monongahaly, Monongaheley, Monongahelia, Monongalia, Monongalo, Mononguhela, Mononyahela, Muddy River

Via the Ohio River, the river is part of the Mississippi watershed which drains to the Gulf of Mexico on the Atlantic Ocean. The river's length is 130 miles, its drainage basin is 7,340 sq. mi. and the average 30 year discharge at Elizabeth, Pennsylvania, is 9,109 cfs. It falls 3,831 ft. in elevation from its highest source to its mouth on the Ohio River. It falls 280 feet from its forks to its mouth, a stretch made navigable by locks. The mean depth is about 20 ft. In southwestern Pennsylvania, the Monongahela is met by two major tributaries: the Cheat River, which joins at Point Marion, and the Youghiogheny River, which joins at McKeesport. Major tributaries include: Becks Run, Big Sandy Creek, Buffalo Creek, Cheat River, Crooked Run, Deckers Creek, Dunkard Creek, Lick Run, Middle Fork River, Paw Paw Creek, Peters Creek, Streets Run, Turtle Creek, Tygart Valley River, West Fork River, Youghiogheny River.

The river is navigable its entire length with a series of locks and dams that maintain a minimum depth of 9 feet (3 m) to accommodate coal laden barges. All dams are operated by the Pittsburgh District Army Corps of Engineers. In 2006, the navigation system, operated by the U. S. Army Corps of Engineers, had nine dam locks along 128.7 mile (207 km) of waterway. The locks overcame a change in elevation of about 147 feet (45 m).

According to the EPA's Toxics Release Inventory for 2010, the Monongahela ranked as the 17th most polluted river in the nation. The primary polluters were Pennsylvania iron and steel mills.

The Monongahela River valley was the site of a famous battle that was one of the first in the French and Indian War—the Braddock Expedition (May–July 1755). It resulted in a sharp defeat for two thousand British and Colonial forces against those of the French and their Native American allies. In 1817, the Pennsylvania legislature authorized the Monongahela Navigation Company to build 16 dams with bypass locks to create a river transportation system between Pittsburgh and the area that would later become West Virginia. Originally planned to run as far south as the Cheat River, the system was extended to Fairmont, and bituminous coal from West Virginia was the chief product transported downstream. After a canal tunnel through Grant's Hill in Pittsburgh was completed in 1832, boats could travel between the Monongahela River and the Western Division Canal of Pennsylvania's principal east–west canal and railroad system, the Main Line of Public Works. In 1897, the federal government took possession of the Monongahela Navigation through condemnation proceedings. Later, the dam lock combinations were increased in size and reduced in number. Briefly linked to the Monongahela Navigation was the Youghiogheny Navigation, a slack water system of 18.5 mile (30 km) between McKeesport and West Newton. It had two dam locks overcoming a change in elevation of about 27 feet (8 m). Opening in 1850, it was destroyed by a flood in 1865. Coal barges are a common sight on the river, and the railways which line either side are heavily used by freight. Other industries include power generation, chemicals, and recycling.

Three ships in the United States Navy have been named Monongahela after the river. In October 1930, severe drought caused the river flow to drop below , and in some places, it was possible to walk across the river bottom. The river was the site of a famous airplane crash that has become the subject of urban legends and conspiracy theories. Early on the morning of January 31, 1956, a B 25 bomber en route from Nellis Air Force Base in Nevada to Olmsted Air Force Base in Pennsylvania crashed into the river near the Glenwood Bridge in Homestead, Pennsylvania. The six crewmen survived the initial crash, but two of them succumbed in the cold water and drowned. Despite the relatively shallow water, the aircraft was never recovered and became known as the "ghost bomber". The Pittsburgh Post Gazette published a graphical representation of the flight path and flight details in 1999. As of 2018, the bomber has not been found.