 The Balkan mountains run laterally through the middle of the country . The mountainous southwest of the country has two alpine ranges — Rila and Pirin , which border the lower but more extensive Rhodope Mountains to the east . Bulgaria is home to the highest point of the Balkan peninsula , Musala , at 2 @,@ 925 metres ( 9 @,@ 596 ft ) and its lowest point is sea level . Plains occupy about one @-@ third of the territory , while plateaus and hills occupy 41 per cent . The country has a dense network of about 540 rivers , most of which are relatively small and with low water levels . The longest river located solely in Bulgarian territory , the Iskar , has a length of 368 kilometres ( 229 mi ) . Other major rivers include the Struma and the Maritsa in the south . 
