The longest river that Bulgaria has a bank on is the Danube (2,888 km), which spans most of the country's northern border. The longest one to run through the country (and also the deepest) is the Maritsa (480 km), while the longest river that runs solely in Bulgaria is the Iskar (368 km).
The Danube is a river in Central Europe, the European Union's longest and the continent's second (After the Volga).
Classified as an international waterway, it originates in the town of Donaueschingen--which is in the Black Forest of Germany--at the confluence of the rivers Brigach and Breg. The Danube then flows southeast for 2,872 km (1,785 mi), passing through four Central European capitals before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.
Once a long-standing frontier of the Roman Empire, the river passes through or touches the borders of ten countries: Romania (29.0% of basin area), Hungary (11.6%), Serbia (10.2%), Austria (10.0%), Germany (7.0%), Bulgaria (5.9%), Slovakia (5.9%), Croatia (4.4%), Ukraine (3.8%), and Moldova (1.6%drainage basin extends into nine more.