The proprietor of any private pond or lake, and the selectmen of any town in which any pond or lake is situated, or the selectmen of the towns surrounding any lake or pond located in more than one town, may, when any such pond or lake has been stocked by the commissioner with bass, landlocked salmon or any other fish not natural to such waters, construct or authorize the construction of weirs or nets to prevent the escape of any such fish and to prevent any such fish from getting into any flume or mill race and being injured or destroyed by any machinery or chemical; provided, when the water of any such pond or lake is used for manufacturing or any other purpose, any such weir or net shall be so constructed and kept clear from obstruction that it shall not interfere with the full passage of water.