33 U.S.C. § 512 : Navigation And Navigable Waters — Bridges Over Navigable Waters — Alteration Of Bridges — Obstruction Of Navigation Date: 7 Mar 2017 TEXT PDF No bridge shall at any time unreasonably obstruct the free navigation of any navigable waters of the United States. (June 21, 1940, ch. 409, § 2, 54 Stat. 498.)