Iowa Code § 468.618: Obstruction.

Any person who shall dam up, obstruct, or in any way injure any ditch or drain so constructed, shall be liable to pay to the person owning or possessing the swamp, marsh, or other lowlands, for the draining of which such ditch or ditches have been opened, double the damages that shall be sustained by the owner, and, in case of a second or subsequent offense by the same person, treble such damages.