Bear Run is a 5.0-mile-long (8.0 km)[6] tributary of the Youghiogheny River in Fayette County, Pennsylvania, United States.

The Fallingwater house, designed by architect Frank Lloyd Wright, is located on this stream at the locality known as Mill Run.

Ohiopyle today is the focal point of tourism in the Laurel Highlands, drawing many of the same visitors as Fallingwater, located a few miles away on PA State Route 381.

[3] Bear Run drains 6.47 square miles (16.8 km2) of area, receives about 48.1 in/year of precipitation, has a wetness index of 357.26, and is about 89% forested.

The large forested area of Bear Run, an exceptional value stream, provides habitat for three plant species of special concern.