Any person who places any material which tends to obstruct navigation in navigable waters shall be fined not more than one hundred dollars, and such person shall be ordered by the court before which the conviction is had to remove such material within thirty days, and, on his failure to do so, any person may remove such material at the expense of the person who placed it there; but the provisions of this section shall not apply to oyster beds that have been designated and set out for the purpose of planting and cultivating oysters thereon. Nothing in this section shall prohibit the filling or wharfing out in such waters between the shore and the harbor lines established in any harbor.