Vertical mooring buoys have been in place at the locks and dams to warn boaters of the dam ahead, but in order to increase warning visibility, the U.S. Army Corps of Engineers Pittsburgh District added horizontal safety buoys at the Allegheny River Lock and Dam 2 and at the Dashields Lock and Dam on the Ohio River in Pittsburgh to help prevent recreational boaters from going over the dam. The dams on the Allegheny River and at Dashields are submerged, also known as fixed crest dams, which make them difficult to see from upstream. (U.S. Army Corps of Engineers Pittsburgh District photo by Michel Sauret)