Oka (river)

Oka (Ока́)
The Oka riverbank in Nizhny Novgorod
Country	Russia
Cities	Oryol, Kaluga, Serpukhov, Kolomna, Ryazan, Murom, Dzerzhinsk, Nizhny Novgorod
Source
- location	Oryol Oblast
- elevation	226 m (741 ft)
- coordinates	52°21′45″N 36°13′20″E / 52.36250°N 36.22222°E / 52.36250; 36.22222
Mouth	Volga River
- location	Nizhny Novgorod
- elevation	67 m (220 ft)
- coordinates	56°19′55″N 43°58′53″E / 56.33194°N 43.98139°E / 56.33194; 43.98139Coordinates: 56°19′55″N 43°58′53″E / 56.33194°N 43.98139°E / 56.33194; 43.98139
Length	1,500 km (932 mi)
Basin	245,000 km2 (94,595 sq mi)
Discharge
- average	1,260 m3/s (44,496 cu ft/s)
Map of the Volga watershed with the Oka highlighted

Oka (Russian: Ока́, IPA: [ɐˈka]) is a river in central Russia, the largest right tributary of the Volga. It flows through the regions of Oryol, Tula, Kaluga, Moscow, Ryazan, Vladimir, and Nizhny Novgorod and is navigable over a large part of its total length, as far upstream as to the town of Kaluga. Its length exceeds 1,500 kilometres (930 mi). The Russian capital Moscow sits on one of the Oka's tributaries—the Moskva River.

Max Vasmer connects the name of the river to the Gothic аƕа, Old High German aha, Latin aqua, which all mean either "water" or "river" (cf. ).Oleg Trubachev traces the origin of the name to the Baltic languages: the Baltic tribe of Galindians lived in the western part of the Oka basin prior to the arrival of the Slavs.

Historically, the river gave its name to the Upper Oka Principalities, situated upstream from Tarusa. In 1221 Grand Duke Yuri II of Vladimir founded Nizhny Novgorod, later to become one of the largest Russian cities, to protect the Oka's confluence with the Volga. The Qasim Khanate, a Muslim polity, occupied the middle reaches of the Oka (around the city of Kasimov) in the 15th and 16th centuries.