The most important river in Thuringia is the Saale (a tributary of the Elbe) with its tributaries Unstrut, Ilm and Weiße Elster, draining the most parts of Thuringia and the Werra (the headwater of the Weser), draining the south-west and west of the Land. Furthermore, some small parts on the southern border are drained by tributaries of the Main (a tributary of the Rhine). There are no large natural lakes in Thuringia, but it does have some of Germany's biggest dams including the Bleiloch Dam and the Hohenwarte Dam at Saale river same as the Leibis-Lichte Dam and the Goldisthal Pumped Storage Station within the Highland. Thuringia is Germany's only state without connection to navigable waterways.
Which tributary is located on the northern border?