§ 120. Dams and bridges. No dam shall be erected on any river or stream in this state, recognized by law or use as a public highway for the purpose of floating and running lumber, logs or other timber, over or upon the same, unless there be built in such dam an apron, at least fifteen feet in width, in the middle of the current of such river or stream, of a proper slope for the safe passage of lumber, logs and other timber. No bridge shall be built over any such river or stream in such a manner as to obstruct or prevent the free and uninterrupted passage of lumber, logs and other timber down and along such river or stream.