Reichenau Island is an island in Lake Constance in southern Germany, at approximately (47°42′N9°4′E). It lies between Gnadensee and Untersee, two parts of Lake Constance, almost due west of the city of Konstanz. The island is connected to the mainland by a causeway that was completed in 1838. The causeway is interrupted between the site of the former castle Schopflen and the eastern end of Reichenau Island by the 10-metre-wide Bruckgraben, a waterway which is spanned by a low road bridge that allows passage of ordinary boats but not of sailboats through its 95-metre course. Its total area is less than 7 square kilometers (3 square miles).