Cottus haemusi in the context of "Iskar River"

The Iskar (Bulgarian: Искър, pronounced [ˈiskɐr]; Latin: Oescus) 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 km in the provinces of Sofia, Sofia City, Vratsa, Lovech and Pleven. The Iskar flows through nine towns and numerous villages. The Iskar river basin is home to more than 50 species of fish, including Cottus haemusi that is endemic to the upper Iskar and Vit drainages.

The Vit (Bulgarian: Вит; Latin: Utus) is a river in northern Bulgaria, a right tributary of the Danube. Its length including the main stem Beli (White) Vit is 189 km, while the river proper, formed by the confluence of the Beli and Cherni (Black) Vit is 153 km. Vit Ice Piedmont in Antarctica is named after the river. The fish species Vit sculpin of the genus Cottus is endemic to the Vit.