Lockport Historic District, Chicago Sanitary & Ship Canal, Butterfly Dam, Lockport, Will County, IL

Significance: The Butterfly Dam was constructed in the middle of the Chicago Sanitary and Ship Canal for the purpose of providing flood protection for Joliet and other points on the canal west of Lockport. The dam is unique in that it is suspended from a Pratt truss bridge which is supported by two concrete piers. The dam is on a pivoting mechanism, so it can be turned to cross the canal and block the flow of water. It is 30 feet high, and has six electrically operated valves on each leaf. The need to use the dam for flood prevention seems never to have arisen.
Survey number: HAER IL-16-C
Building/structure dates: ca. 1903 Initial Construction