The Osam ( ) is a river in northern Bulgaria, a right tributary of the Danube. Its length including the main stem Cherni (Black) Osam is 314 km, making it the fifth longest river in Bulgaria. The river proper, formed by the confluence of the Cherni and Beli (White) Osam, is 278 km.
Geography
Course
thumb|left|Gorge of the Cherni Osam
thumb|left|The Osam at [[Troyan]]
The main stem the Cherni Osam is 36 km long and takes its source at an altitude of 1,880 m on the southwestern foothills of the summit of Levski (2,166 m) in the Balkan Mountains and flows north. The other stem, the 28 km long Beli Osam, springs at an altitude of 1,560 m northeast of the summit of Ushite (1,637 m) in the Troyan section of the Balkan Mountains and flows northeast in a deep forested valley.
The river proper forms by the confluence of the Beli Osam (left branch) and the Cherni Osam (right branch) at an altitude of 371 m in the northern outskirt of the town of Troyan. It flows north to the town of Lovech and then turns northeast until the town of Levski. In the fore-Balkan between Troyan and Aleksandrovo the Osam flows in a deep ravine-like valley. Downstream of Aleksandrovo the river enters the Danubian Plain, forming an asymmetrical valley with steeper right and gentle left slopes. From Levski the Osam's general direction is northwest. The riverbed widens and due to the small gradient meanders in all directions. In this section the riverbed is corrected with water protection dikes; the bottom changes from stony to sandy. It flows into the Danube at an altitude of 22 m between the town of Nikopol to the east and the village of Cherkovitsa to the west. and the Lomya (39 km).
The Osam has a mixed feed of snow, rain and karst waters. Snow and rain feed is prevalent in the Balkan Mountains and the fore-Balkan, rain in the Danubian Plain and underground karst water in the fore-Balkan.
Along the left bank of the Osam passes a section of railway line Levski–Lovech–Troyan served by the Bulgarian State Railways.
Landmarks
The upper reaches of the Osam fall within the boundaries of the Central Balkan National Park. The upper valley of the Cherni Osam and its gorge in particular is part of the Steneto Reserve. That area is known for its numerous limestone caves, including Raychova Dupka which is the second deepest cave in Bulgaria with a depth of -377 m. Along the left bank of the Cherni Osam south of the village of Oreshak is located the Troyan Monastery, among the largest and most important spiritual sites in the country.
Further downstream in Lovech, the river is crossed by the 19th century Covered Bridge and is overlooked by the Lovech Fortress, a major medieval Bulgarian stronghold. On the high right shore of the Osam near the village of Devetaki is located the Devetashka cave, one of the country's most picturesque caves. Along its tributary the Maarata near the village of Krushuna are the Krushuna Falls, an attractive travertine cascade.
Gallery
<gallery mode="packed">
File:Osam River857105.JPG | The Osam through the Devetashko Plateau
File:Каньон на река Осъм, Ловеч - Osam River Canyon, Lovech - panoramio (1).jpg| Near Lovech
File:Devetashka cave 4.jpg | Devetashka cave near the banks of the Osam
</gallery>