Rush Brook is a tributary of the Lackawanna River in Lackawanna County Pennsylvania in the United States. It is approximately 5.1 miles (8.2 km) long and flows through Greenfield Township Scott Township Carbondale Township Mayfield and Jermyn. The watershed of the stream has an area of 6.01 square miles (15.6 km2). The stream is not considered to be impaired and all but its lower reaches are mostly undisturbed. However Pennsylvania Route 107 is in its vicinity. The stream begins on the Allegheny Plateau and flows through a water gap. It is a perennial stream.