Prohibits the Department of the Army from promulgating or enforcing any regulation that prohibits an individual from possessing a firearm in any area open to the public (other than a federal facility) at a water resources development project administered by the Chief of Engineers if: (1) the individual is not otherwise prohibited by law from possessing the firearm, and (2) the possession of the firearm is in compliance with the law of the state in which the project is located.