[1] 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.

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 was Olše.

[8] The Olza forms two sections of the Czech-Polish state border with a total length of 25.3 km (15.7 mi).

According to the newest official measurements, the Czech part of the river (including the Czech-Polish state border) is 73.1 km (45.4 mi) long.

The river then continues through the territories of Karviná, Dětmarovice and Petrovice u Karviné before it begins to form the state border again, which lasts until its mouth.

In this section, it flows along the territories of Godów and Gorzyce in Poland and Dolní Lutyně and Bohumín in the Czech Republic.

The river is 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.