Benton City - Fry Rec Area.
The upside of this caches location is that it shouldn't float away if the area floods. The downside it that its very close to the park boundary, so if you get 'there' and think you should cross that fence... DON'T. Also, the park is closed to visitors (non-camping persons?) from 10pm to 6am.
Note: Depending on how you approach the cache you may pass close to camping site(s) (most likely *Hill Topping* 21&22 if any), if there happen to be persons camping there, please be courteous.
For more on geocaching in Iowa, vist the Iowa Geocachers Organization home page.