Iowa Code § 420.165
With respect to any lands title to which has been or may be granted by the state to any municipal corporation of the state, acting under special charter, sections 327F.4 and 327F.5 shall not, after the occurrence of such grant, continue to apply, excepting only that permanent structures erected prior to such grant under authority of said section 327F.4 may continue to be used, occupied, and maintained thereunder, and excepting further only that such lands may continue to be used and occupied thereunder, to the extent only that use and occupancy of such lands shall be necessary to the use and occupancy of such structures for like purposes and in like manner as before such grant; provided that nothing herein contained shall be deemed to affect riparian rights at common law.
Iowa Code § 420.165