The Danube River is one of the longest rivers in Europe, and it has many tributaries. Two of these tributaries are the Tisza and the Osage. The Tisza is a river that flows through Hungary, Ukraine, Romania, and Serbia. It is 545 miles long and is the second longest tributary of the Danube. The Osage is a tributary of the Missouri River in the United States. It is 545 miles long and is the longest tributary of the Missouri River.