Idaho Code § 42-1205
All owners of any ditch, canal or conduit, or any other means for conveying water, shall build substantial bridges not less than sixteen (16) feet wide, and with boards not less than two (2) inches in thickness (unless the same shall be on a county or state road, when such boards shall not be less than three (3) inches thick), at all places where any county or state road crosses the same, or any road kept open and used by any neighborhood of people for their benefit and convenience. In case of neglect or refusal of such owners to build such bridges as above required, after a notice of ten (10) days being given by the said board of county commissioners of the proper county, said board shall proceed to the construction of the same, and shall collect the cost thereof together with the costs of suit: provided, that after any bridge shall have been constructed across any ditch, canal or conduit on any county or state road in accordance with the provisions of this section, it shall thereafter be maintained at the public expense.
Idaho Code § 42-1205