The term RIVER TO THE DANUBE refers to a series of rivers that flow into the Danube, the second longest river in Europe. The rivers include the LECH (4 letters), which is a tributary of the Danube that originates in the Austrian Alps; the INN (3 letters), which is a major tributary of the Danube that flows through Austria and Germany; the Enns (4 letters), which is a tributary of the Danube that flows through Austria; the Isar (4 letters), which is a tributary of the Danube that flows through Germany; the Prut (4 letters), which is a tributary of the Danube that flows through Romania and Ukraine; the Raba (4 letters), which is a tributary of the Danube that flows through Hungary and Slovakia; the Tisa (4 letters), which is a tributary of the Danube that flows through Hungary, Romania, and Ukraine; and the Siret (5 letters), which is a tributary of the Danube that flows through Romania.