The purposes of this section are to prevent and control water pollution; protect spawning grounds, fish and aquatic life, and to preserve shore cover and natural beauty. The provisions of this section shall apply to the shore lands of all navigable waters. All lakes, ponds, or flowages of one-half (½) acre or more shall be considered navigable for the purposes of this chapter and rivers and streams shall be considered navigable for the purpose of this chapter if they are indicated as "continuous" on the United States Geological Quadrangle Survey Maps. Watercourses of less than three (3) acres shall provide a sixty-foot set back from the water and watercourses of three (3) acres or more shall provide a seventy-five-foot set back from the water.