All reservoir sites reserved or to be reserved shall be open to use and occupation under sections 946 to 949 ¹ of this title, and any State is authorized to improve and occupy such reservoir sites to the same extent as an individual or private corporation, under such rules and regulations as the Secretary of the Interior may prescribe: Provided, That the charges for water coming in whole or part from reservoir sites used or occupied under the provisions of this section shall always be subject to the control and regulation of the respective States and Territories in which such reservoirs are in whole or part situate.