Charleroi Locks & Dam, officially known as Locks & Dam 4 by the US Army Corps of Engineers, is one of nine navigational structures on the Monongahela River between Pittsburgh, Pennsylvania and Fairmont, West Virginia. Maintained and built by the U.S. Army Corps of Engineers, the gated dam forms an upstream pool that is for 19.7 miles to the Maxwell Lock & Dam. The dam is located at mile 41.5 on the river. Unlike many of the river's single lock structure, the Charleroi facility features two working locks; this addition took place during a 1967 rehabiliation project.