The Olza (, ) is a river in the Czech Republic and Poland, a right tributary of the Oder River. It flows through the Silesian Voivodeship in Poland and through the Moravian-Silesian Region in the Czech Republic. It is long. The river forms a significant part of the Czech-Polish state border.
Etymology
The name is derived from the Proto-Slavic word oliga, meaning "a river rich in water". The origin of the name was demonstrated in 1900 by Czech linguist and writer Vincenc Prasek and the revelation was confirmed by various etymological studies in the 20th century. There was also a theory that the name is a derivative of the Germanic Aliza, meaning 'flow'. The river was then mentioned in a written document in 1611 as the Oldza. At the end of the 19th century, with the rise of mass nationalism, both Polish and Czech activists claimed the name Olza to be not Polish enough, on the one hand, and insufficiently Czech, on the other. of which is in the Czech Republic. The average discharge at its mouth is .
The Olza forms two sections of the Czech-Polish state border with a total length of . Length figures vary by source. According to the newest official measurements, the Czech part of the river (including the Czech-Polish state border) is long. The length of the Polish section of the river to the first crossing of the state border is usually stated as , which means that according to the latest measurements, the river has a total length of . However, based on older measurements, the total length of the river is stated as ,