Olza (river)
The (, ) is a river in Poland and the Czech Republic, a right (eastern) tributary of the River Oder. It flows from the Silesian Beskids mountains through southern Cieszyn Silesia in Poland and the Frýdek-Místek and Karviná districts of the Czech Republic, often forming the border with Poland. It flows into the Oder River north of Bohumín. The Olza-Oder confluence also forms a part of the border. The river is a symbol of the Zaolzie () region, which lies on its west bank, constituting a part of the western half of Cieszyn Silesia, as depicted in the words  of the unofficial anthem of this region and of local Poles, "Płyniesz Olzo po dolinie" (Thou flowest, Olza, down the valley), written by Jan Kubisz. The Olza has also inspired many other artists. Among those who have written about the river are Adolf Fierla, Pola Gojawiczyńska, Emanuel Grim, Julian Przyboś, Vladislav Vančura, and Adam Wawrosz. The singer Jaromír Nohavica has used the Olza as a motif in several of his songs. Name. The oldest surviving written mention is in a letter dating from 1290, which refers to the river "Olza". 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. Some Polish activists proposed the name "Olsza", Czech activists "Olše". The Czech linguist and writer Vincenc Prasek demonstrated in 1900 that the name "Olza" has, in fact, an independent Old Slavic origin which predates both Polish and Czech. This revelation has been confirmed by various etymological studies in the 20th century. The regionally used form "Olza" is derived from  the ancient "Oldza". German "Olsa" is a re-spelling of "Olza" but pronounced the same. Local people always used the "Olza" form, regardless of their national or ethnic origin. However, the central administration in Prague saw "Olza" as a Polish name and when most of the river became a part of Czechoslovakia in 1920 it tried to change its name to the Czech form, "Olše". However, a degree of dualism in the naming persisted until the 1960s, when the Central State Administration of Geodesy and Cartography ruled that the only official form in the Czech Republic is "Olše". Locals on  both sides of the border and from both nationalities continue to refer to the river as the "Olza" nevertheless. Towns and villages on the river. "(from source to the mouth)"