South Carolina Code 4-3-5. Center line of waterways defined
(1) for areas influenced by the tide, the center line is the line described by a series of points equidistant from the banks as delineated at mean high tide, except when an island is present; then the center line follows the main channel around the island and is the line described by a series of points equidistant from the banks of the main channel as delineated at mean high tide; and
(2) for areas not influenced by the tide, the center line is the line described by a series of points equidistant from the banks as delineated by the ordinary high-water mark, except when an island is present; then the center line follows the main channel around the island and is the line described by a series of points equidistant from the banks of the main channel as delineated by the ordinary high-water mark.