Beaver River is a tributary of the Ohio River in Western Pennsylvania. Approximately 21 mi (34 km) long, it flows through a historically important coal-producing region north of Pittsburgh. The river is formed in Lawrence County by the confluence of the Mahoning and Shenango rivers in the Mahoningtown neighborhood of New Castle. It flows generally south, past West Pittsburg and Homewood, then receives Connoquenessing Creek west of Ellwood City and flows past Beaver Falls and New Brighton. It joins the Ohio at Bridgewater and Rochester at the downstream end of a sharp bend in the Ohio approximately 20 mi (32 km) northwest of Pittsburgh. In the lower reaches near the Ohio River, the Beaver cuts through a gorge of underlying sandstone. The river is roughly parallel to the border with the state of Ohio, with both Interstate 376 and Pennsylvania Route 18 running parallel to the river itself.

The Mahoning River is a river in northeastern Ohio and a small portion of western Pennsylvania. Flowing primarily through several Ohio counties, it crosses the state line into Pennsylvania before joining with the Shenango River to form the Beaver River. The Mahoning River drops from 1,296 feet (395 m) at the headwaters near Winona to 761 feet (232 m) at the outfall near Mahoningtown, Pennsylvania. It is part of the Ohio River watershed. The name is said to derive from either the Lenape or Shawnee languages and mean "Deer Lick," as the area was once known for salt springs, but it's possible the name of the Mahoning and several other similarly named landmarks and places in western Pennsylvania could come from the Lenape, mënehokink (may-nuh-ho-keeng), meaning "place to get water."