The submerged dam, also known as a fixed crest dam, at the Allegheny River Lock and Dam 2 is difficult to see from upstream and can be dangerous if boaters navigate too closely to it. The Pittsburgh District recently added horizontal buoys on the Allegheny and at the Dashields Lock and Dam on the Ohio River to provide even more visible signs to warn recreational boaters from going over the dam. (U.S. Army Corps of Engineers Pittsburgh District photo by Michel Sauret)