The lines of the several counties of the State which terminate at or in tidewaters shall run by the principal channel in such directions as to include, within the counties to which they belong, the several islands in said waters, and after so including such islands shall run in the shortest and most direct line to the extreme limit of the waters under the jurisdiction of this State, and all waters between such lines off the shores of the respective counties shall be a part of, and held to be within, such counties, respectively.