Iowa Code § 462A.30: Aircraft restriction.

It is unlawful for any aircraft to make use of the inland lakes of the state, except in the transportation of persons or property between points separated by a distance of thirty miles or more. However, this section does not prohibit the use of such waters by any aircraft in danger or distress or the use of such waters by the operators of private aircraft, not operated for hire. In addition, the commission may, on the recommendation of the state department of transportation, designate certain areas on inland lakes of the state where seaplane flight instruction may be conducted under such conditions as may be adopted by the commission and the state department of transportation.