There are more than 1 200 rivers in Bulgaria. Most of them are small and only 30 of them are longer than 100 km. The Iskar River is the longest Bulgarian river flowing only on the territory of Bulgaria. It is 368 km long. The rivers in Bulgaria are flowing into the Black Sea (56%) and the Aegean Sea (44%). There are more than 400 lakes and marshes. They are most abundant in the Rila and Pirin Mountains - 360. Most of them have a glacial origin and lie at an altitude of 2000-27000 m. Their size is small and their depth varies from 2 to 3,75 m. The Okoto Lake in Rila and Popovoto Lake in Pirin are 29,5 m deep. The biggest Bulgarian rivers Maritza, Iskar and Mesta spring from these lakes.

Bulgaria abounds in mineral springs. The average annual capacity is 109 million cubic metres. However, only half of them are used. The temperature range of the springs is between 8^oC and over 100^oC. The hottest mineral spring in Bulgaria is Sapareva Banya with a temperature of 103,5 ^oC.