That any corporation now in existence, or which may hereafter be organized under any law of this state, having as its object the clearing out and improving of any river or stream navigable only for the purpose of driving logs and floating timber within the state, for the purpose of driving, sorting, holding and delivering logs thereon, which has taken possession of such stream, and made permanent and valuable improvements thereon by clearing and straightening the channels thereof, closing sloughs, erecting sluiceways or building dams, as may be required; or where individuals have made such improvements, with the intention of subsequently incorporating, such corporation or individuals shall have the right to control such stream, under such restrictions and in the manner following: Provided, That in all cases where individuals have already made improvements upon any stream or streams they shall proceed to incorporate under the laws of this state, within 4 months from the passage of this act.