The Vltava is the longest river in the Czech Republic, flowing for 270 miles (430 km) across the country. Known as the “Czech national river,” it begins near the southern border and travels north across Bohemia, passing through Prague before merging with the Elbe in the city of Mělník. The river has a basin of more than 10,800 square miles (28,000 square km), which is about a third of the Czech Republic’s entire territory.