The commissioner may establish a line at the outlet and inlet of any artificial or natural lake or pond, which line shall divide such lake or pond from any stream or river flowing into or out of the same. On one side of such line the provisions of this chapter relating to fishing in lakes and ponds shall apply and on the other side of such line the provisions of this chapter relating to fishing in rivers or streams shall apply, as the case may be. Such line shall be fixed by posts suitably marked as the commissioner may determine and set upon opposite banks of any such lake, pond, river or stream.