Mo. Rev. Stat. § 236.260

If the improvement of the navigation of any stream shall be undertaken by the state, or by any county, or other lawful authority under the state, then the privilege of keeping any dam across such stream, the right to construct which may be hereafter granted, shall cease, if the same would prevent or obstruct the making of such improvement; and it shall be the duty of the owner or owners of such dam, either to remove it or to make such change in the same as will render the navigation safe and convenient, according to the plan of such improvement; said change or alteration in such dam shall be so constructed as to be approved of by the proper officers or agents who shall have the superintendence of the improvement of such stream.