(1) The owner of a ditch or other watercourse may not alter its course or width, if the land on the opposite bank belongs to another person.
(2) If the land on both banks belongs to the owner of a water course, such owner may alter its course and width; provided, the water shall be restored to its natural course at the lower exit.
(3) If there exists any custom different from those provided for in the preceding two paragraphs, such custom shall prevail.