In all cases where the rights of owners of land in this state to which water rights on interstate streams are appurtenant have been the subject of litigation in the state or federal courts of an adjoining state, it shall be the duty of the state engineer to assume control of all or any part of such interstate stream and of the diversion and distribution of the waters thereof and to administer the same in the public interest; provided, however, that this section shall not apply to conservancy districts, irrigation districts or federal reclamation projects in this state.