The Danube is one of Europe's longest rivers, and it has many tributaries. The crossword solutions for the term 'Danube Tributary' include Iller (5 letters), Siret (5 letters), Isar (4 letters), Vah (3 letters), Drava (5 letters), Olt (3 letters), Enns (4 letters), Hron (4 letters), Temes (5 letters), and Tisza (5 letters). All of these rivers are tributaries of the Danube, and they flow through countries such as Germany, Romania, Hungary, and Austria.