Iowa Code § 1.7

There is hereby granted to the government of the United States, so long as it shall use the same as a part and for the purposes of the said “Upper Mississippi River National Wildlife and Fish Refuge”, all areas of land subject to overflow and not used for agricultural purposes or state fish hatcheries or salvaging stations, owned by this state within the boundaries of the said refuge, as the same may be established from time to time under authority of the said Act of Congress.