The Opava is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in the north-eastern Czech Republic

Czech Republic

The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....

, a left tributary of the Oder

Oder

The Oder is a river in Central Europe. It rises in the Czech Republic and flows through western Poland, later forming of the border between Poland and Germany, part of the Oder-Neisse line...

 river. It originates at the confluence of Bílá (White), Střední (Middle) and Černá (Black) Opava in Vrbno pod Pradědem

Vrbno pod Pradedem

Vrbno pod Pradědem is a town in the Moravian-Silesian Region, Czech Republic. It is located on the Opava River and has 6,072 inhabitants.According to the Austrian census of 1910 the town had 3,614 inhabitants, 3,519 of whom had permanent residence there. Census asked people for their native...

 and runs over 119 km (74 mi) to the Oder at Ostrava

Ostrava

Ostrava is the third largest city in the Czech Republic and the second largest urban agglomeration after Prague. Located close to the Polish border, it is also the administrative center of the Moravian-Silesian Region and of the Municipality with Extended Competence. Ostrava was candidate for the...

, with some 25 km (16 mi) forming the border with Poland

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

.

After the 1742 First Silesian War

Silesian Wars

The Silesian Wars were a series of wars between Prussia and Austria for control of Silesia. They formed parts of the larger War of the Austrian Succession and Seven Years' War. They eventually ended with Silesia being incorporated into Prussia, and Austrian recognition of this...

 the Opava river in the Duchy of Troppau

Duchy of Troppau

The Principality or Duchy of Troppau or Opava was based for centuries around the Upper Silesian city of Troppau . In the final four centuries of its existence, the Duchy belonged to the Austrian Habsburg dynasty, and it was dissolved with the Habsburg Empire in 1918...

 by the terms of the Treaty of Breslau

Treaty of Breslau

The Treaty of Breslau was a preliminary peace agreement signed on 11 June 1742 following long negotiations at the Silesian capital Wrocław by emissaries of Archduchess Maria Theresa of Austria and King Frederick II of Prussia ending the First Silesian War....

 became the border between Austrian

Austrian Silesia

Austrian Silesia , officially the Duchy of Upper and Lower Silesia was an autonomous region of the Kingdom of Bohemia and the Austrian Empire, from 1867 a Cisleithanian crown land of Austria-Hungary...

 and Prussian

Kingdom of Prussia

The Kingdom of Prussia was a German kingdom from 1701 to 1918. Until the defeat of Germany in World War I, it comprised almost two-thirds of the area of the German Empire...

 Silesia (the later Province of Silesia

Province of Silesia

The Province of Silesia was a province of the Kingdom of Prussia from 1815 to 1919.-Geography:The territory comprised the bulk of the former Bohemian crown land of Silesia and the County of Kladsko, which King Frederick the Great had conquered from the Austrian Habsburg Monarchy in the 18th...

). After World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 the demarcation was confirmed by the 1919 Treaty of Saint-Germain-en-Laye as the border between Czechoslovakia

Czechoslovakia

Czechoslovakia or Czecho-Slovakia was a sovereign state in Central Europe which existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until 1992...

 (Czech Silesia

Czech Silesia

Czech Silesia is an unofficial name of one of the three Czech lands and a section of the Silesian historical region. It is located in the north-east of the Czech Republic, predominantly in the Moravian-Silesian Region, with a section in the northern Olomouc Region...

) and the Second Polish Republic

Second Polish Republic

The Second Polish Republic, Second Commonwealth of Poland or interwar Poland refers to Poland between the two world wars; a period in Polish history in which Poland was restored as an independent state. Officially known as the Republic of Poland or the Commonwealth of Poland , the Polish state was...

.

Towns

• Vrbno pod Pradědem
  Vrbno pod Pradedem
  Vrbno pod Pradědem is a town in the Moravian-Silesian Region, Czech Republic. It is located on the Opava River and has 6,072 inhabitants.According to the Austrian census of 1910 the town had 3,614 inhabitants, 3,519 of whom had permanent residence there. Census asked people for their native...
  
  
• Krnov
  Krnov
  Krnov is an Upper Silesian city in the northeastern Czech Republic, in the Moravian-Silesian Region, the District of Bruntál, on the Opava River, near the Polish border....
  
  
• Opava
  Opava
  Opava is a city in the northern Czech Republic on the river Opava, located to the north-west of Ostrava. The historical capital of Czech Silesia, Opava is now in the Moravian-Silesian Region and has a population of 59,843 as of January 1, 2005....
  
  
• Kravaře
  Kravare
  Kravaře is a town in Silesia in the Czech Republic. It has 6,650 inhabitants. It is located between Ostrava and Opava . It is part of the Hlučínsko micro-region.-History of the town:The first historical record of Kravaře is from 1224...
  
  
• Ostrava
  Ostrava
  Ostrava is the third largest city in the Czech Republic and the second largest urban agglomeration after Prague. Located close to the Polish border, it is also the administrative center of the Moravian-Silesian Region and of the Municipality with Extended Competence. Ostrava was candidate for the...