The Vltava river is the natural axis of the southern half of Bohemia. The source of the river is in Šumava under the Černá mountain at a height of 1,172 metres above sea level. First of all it flows south-east and on the border of the Trojmezenská and Českokrumlovská highlands it turns northwards. The length of its flow to the mouth of the river to the Labe river near Mělnik is 430.2 km. Down to Český Krumlov it has a catchment area of 1,339 km2, the whole basin of the Vltava river is 28,090 km2. In the town of Vyšší Brod the average long-term annual rate of flow is 13.6 m3s-1, in Český Krumlov 18.5 m3s-1, the highest registered water level measured on a water gauge in the town was 432 cm, the lowest 61 cm. The highest rate of flow recorded here was 210 m3s-1 (in May 1949) and the lowest recorded 1.7 m3s-1 (in December 1934). In Praha the average rate of flow of the Vltava river is 145 m3s-1 and at the mouth of the river to the Labe river the rate of flow is 150 m3s-1.