Iskar (river)

The Iskar (, ; ) is a right tributary of the Danube. With a length of 368 km, it is the longest river that runs entirely within Bulgaria. Originating as three forks in Balkan's highest mountain range Rila, the Iskar flows in a northern direction until its confluence with the Danube. As it flows northwards it fuels the largest artificial lake in the country, the Iskar Reservoir, forms the divide between the Vitosha and Plana Mountains in the west and the Sredna Gora mountain range in the east before entering the Sofia Valley, which contains the nation's capital Sofia. From there the Iskar runs through the Balkan Mountains, forming the spectacular 84 km long Iskar Gorge. As it crosses the mountains, its water course turns in a north-eastern direction at Lakatnik. North of the Balkan Mountains, the river crosses the Danubian Plain and finally flows into the Danube between the villages of Baykal and Gigen. Geologically, Iskar is the oldest river in the Balkan Peninsula.

Its watershed drains 8,617 km² The Danube and the Maritsa rivers are both longer but they also flow through other countries. The Iskar is a tributary to the Danube and forms part of the Black Sea river basin. It is the only river that takes its source in southern Bulgaria and flows north through the Balkan Mountains that form the water divide between the basins of the Black Sea to the north and the Aegean Sea to the south. In terms of geology, the Iskar is the oldest river in the Balkans and also the only one to have preserved its original direction despite the significant geological changes in later stages. The Iskar basin spans a territory of 8,646 km² in six Bulgarian provinces, Sofia, Sofia City, Vratsa, Lovech and Pleven, with a total population of about 1,600,000 people. Malki Iskar (85 km) and Zlatna Panega (50 km); the largest left tributaries are the Palakaria (39 km), Vitoshka Bistritsa (12 km) and Perlovska (31 km). Its average discharge at the mouth is .

Course

Upper course

thumb|left|alt=a glacial lake|One of the glacial [[Musala Lakes in the Rila mountains that feeds the uppermost tributaries of the Iskar]]

The Iskar headwaters consist of three forks in the northern slopes of Rila, Bulgaria's highest mountain range. The 23 km long Cherni (black) Iskar is considered the main stem of the river. It takes its source from the Chamovsko Lake (2,500 m) to the north-east of the summit of Damga (2,669 m) and from there the river flows in north-eastern direction through the Govedartsi Valley, fuelled by the waters of the Chanakgyolski, Malyovishki and Urdini Lakes. Cherni Iskar's discharge at Goverdartsi is 1.60 m³/s; its basin covers 237 km². It forms a deep and steep valley and has a basin of 91 km². One of its tributaries, the Musalenska Bistritsa, takes its beginning from the Musala Lakes under the slopes of Musala (2,925 m), the highest summit of the Balkan Peninsula. In its upper course at an altitude of 1,900 m is located the Beli Iskar Reservoir, constructed between 1939 and 1945, that powers a small 16 MW hydro power station. It flows through a deep valley for 18 km until its confluence with Cherni Iskar downstream of the village Mala Tsarkva and has a watershed of 56 km². Downstream of the dam the Iskar flows in north-western direction and forms the 22 km long Pancharevo Gorge that divides the Vitosha and Plana Mountains in the west and the Sredna Gora mountain range in the east. There it fills the Pasarel Reservoir and Lake Pancharevo.

Middle course

thumb|right|upright=2.6|alt=a panorama of the Iskar Gorge|Panoramic view of the [[Iskar Gorge]]

The middle course of the Iskar takes its beginning at the village of German. In the southern parts of the valley the Iskar has an inclination of 6.7‰ that decreases to 0.06‰ in the northern reaches of the valley near the town of Novi Iskar. The Iskar Gorge reaches a length of 70 km between its beginning at Kurilo, a neighbourhood of Novi Iskar, and the village of Lyutibrod which marks its end. and the lower course of the Iskar in the vicinity of the town of Dolni Dabnik under the code Iskar River BG0000613.

Ecology

thumb|right|alt=a river|The Iskar near [[German, Bulgaria|German]]

thumb|right|alt=a river|Iskar passing through the Balkan Mountains

The autochthonous ichthyofauna consists of at least 50 species of two classes, Cephalaspidomorphi (jawless fishes) and Actinopterygii (ray-finned fishes), and five orders, Petromyzontiformes (lampreys), Siluriformes (catfish), Gadiformes, Esociformes (pikes and allies) and Perciformes. Many of them are restricted to the lower course near the confluence with the Danube. The jawless fishes of the order Petromyzontiformes are represented by a single family Petromyzontidae with two species, brook lamprey, Carpathian brook lamprey. The only freshwater fish of the order Gadiformes, the burbot, inhabits the lower course near the Danube, which is among the southernmost points of its range. The Esociformes are also represented by a single species, the northern pike.

The Perciformes are the most diverse order of fishes in the Iskar, represented by several families. The autochthonous species of the family Percidae include pikeperch, Volga pikeperch, common zingel, Balon's ruffe, tench, riffle minnow, white-eye bream, sabrefish, European chub, European bitterling, common minnow, common rudd, Kessler's gudgeon, Romanian barbel, The Nemacheilidae are represented by the stone loach, while the species of the family Cobitidae include European weather loach, Balkan loach, golden spined loach, The brown trout is the only representative of the Salmonidae. The predominantly marine family Clupeidae is represented by the Pontic shad. The Gobiidae include Kessler's goby, monkey goby

The Iskar used to be inhabited by one of the six species of sturgeons native to Bulgaria, the sterlet. It could be found upstream as far south as the town of Lukovit but has been extinct from the river and inhabits only the Danube.

The amphibians are represented by frogs, such as the European fire-bellied toad, yellow-bellied toad, European green toad, agile frog, European tree frog, common spadefoot, as wells as by two newt species—Danube crested newt and Balkan crested newt.