The commission may establish the ordinary high-water mark or the ordinary low-water mark of any of the swamp, overflowed, marsh, tide, or submerged lands of this State, by agreement, arbitration, or action to quiet title, whenever it is deemed expedient or necessary. The amendment hereby made is declaratory of the existing law and any such agreements heretofore made establishing the ordinary high-water mark or the ordinary low-water mark of any of the swamp, overflowed, marsh, tide, or submerged lands of this State hereby are ratified and confirmed.