Section 12. The department may license and prescribe the terms for the construction or extension of a dam, road, bridge, or other structure, or the filling of land, the driving of piles, or the making of excavations, in, over, or upon the waters below high water mark of the Connecticut river or of that part of the Westfield river, in the towns of West Springfield and Agawam, lying between the confluence of said river with the Connecticut river and the bridge across said river at Suffield street in the said town of Agawam, and in, over and upon the waters of the non-tidal part of the Merrimack river below high water mark; and the provisions of this chapter shall apply to all such licenses. Every erection made, and all work done on or within the banks of the Connecticut river, of said part of the Westfield river or of said part of the Merrimack river, below high water mark, not authorized by the general court or by the department, or made or done in a manner not sanctioned by the department, without a license as hereinbefore provided, shall be considered a public nuisance. The attorney general and the district attorneys within their respective districts shall, at the request of the department, institute proceedings to enjoin or abate any such nuisance. This section and any such license shall not impair the legal rights or remedies of any person.