Allegheny River Lock and Dam No. 4
 The Allegheny River Lock and Dam No. 4 in Harrison Township Allegheny County Pennsylvania is a lock that was built 1920-1927 and opened in 1927 24.2 miles upsteam from the mouth of the river in Pittsburgh. The lock and dam were built by the U.S. Army Corps of Engineers as a part of an extensive system of locks and dams to improve navigation along the Allegheny River. It has a single lock and a fixed crest dam keeping the river depth at least 9 feet in the pool above the dam.