Every master or mate, or other officer or other person, belonging to or in charge of any vessel, who shall discharge or cause to be discharged the ballast of such vessels into the navigable portions or channels of any of the inlets, bays, harbors or rivers within or bordering on this state, where the water is less than twenty fathoms deep, shall, on conviction thereof, be fined in any sum not less than seventy-five dollars, nor more than five hundred dollars: PROVIDED, That nothing in this section shall be so construed as to prevent any such person from discharging ballast from such vessel on the beach at or above ordinary high tide in all waters where the tide ebbs and flows, and that no ballast shall be discharged on any of the flats included within the boundary of any city or townsite or extension thereof: AND PROVIDED FURTHER, That in harbors within or in front of any incorporated city, where the waters are less than twenty fathoms deep, a section of said harbor may be set aside and designated by the city council of said city as a ballast ground, where ballast may be discharged under control of a harbor master to be appointed by the council.