Idaho Code § 62-106
Any railroad corporation heretofore duly organized and incorporated under the laws of this state, or of the United States, or of any other state or territory, or which may hereafter be duly incorporated and organized under the laws of this state, or of the United States, or of any other state or territory, and authorized to do business in this state and to construct and operate railroads therein, shall have, and hereby is given, the right to build and construct, possess and own, bridges across the navigable streams and waters within this state, over or across which the projected line or lines of railway of such railroad corporation, or either of them, will run: provided, that said bridges are to be constructed in good faith for the purpose of being made a part of the constructed line of said railroad, or a part of any of the line thereof to be constructed and in course of construction, and to be used by such railroad corporation as a part of its line of railroad so constructed, or to be constructed, for the more convenient, expeditious and safe operation thereof: provided further, that such bridges shall be so constructed as to not interfere with, impede or obstruct the navigation of such stream or navigable waters, and shall comply with, and be subject to, the acts of congress relating to navigable streams, and the rules and regulations of the executive departments.
Idaho Code § 62-106