Section 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.