The largest catchment area is the North Sea, covering 51.399 square kilometers, while the smallest is the Baltic Sea - 4721 square kilometers.
The longest river flowing through the Czech Republic is the Elbe, which is 370 km long within the country's borders. Its longest tributary is the Vltava, which flows through the country's capital - it belongs to the North Sea basin.
The longest river in the Black Sea basin is the Morawa, which is 246 km long. The Baltic Sea catchment area includes the Oder, which has its sources in the Czech Republic, and within the borders of this country, its length is 135 km.
