Idaho Code § 70-1504

Port districts shall have full power and authority to regulate and control all navigable and non-navigable waters of the United States and of the state of Idaho, so far and to the full extent that this state can grant the same, within and adjacent to the boundaries thereof, when necessary to the efficient development and operation of the port district; and to that end may straighten, widen, deepen, and otherwise improve any and all such waterways, waters, water courses, bays, lakes, streams or other waters, whether navigable or otherwise, and may create or improve new waterways.