The board of county commissioners is authorized and directed to remove from the tax rolls and to declare as exempt from taxation all inundated lands upon which the owner thereof has granted or hereafter shall grant a permanent easement to the United States of America, its instrumentalities, or agencies, for the purpose of constructing, maintaining, and operating water or wildlife conservation projects, and all lands upon which the owner thereof has granted or hereafter shall grant an easement for a highway or road right of way to the United States, its instrumentalities or agencies, or to the state or its political subdivisions, and such lands so removed from the tax rolls shall remain exempt until such time as such water or wildlife conservation projects or highway shall have been abandoned. Such lands shall not be removed from the tax rolls and declared exempt from taxation until such time as the construction of such water or wildlife conservation projects or highway thereon shall have been completed.