[4][5] It rises in the Jizera Mountains, near Nová Ves nad Nisou, at the Czech border becoming the Polish–German border for its remaining 197 kilometres (122 mi), to flow into the similarly northward-flowing Oder from the left.

[6] The river reaches the tripoint of the three nations by Zittau, a German town/city, after 54 kilometres (34 mi), leaving the Czech Republic.

[6] It is a left-bank tributary of the Oder, into which it flows between Neißemünde-Ratzdorf and Kosarzyn – north of the towns of Guben and Gubin.

The river was a motivations to found Gubin as a craftmanship and trading port in the 13th Century.

[7] Since the 1945 Potsdam Agreement in the aftermath of World War II, the river has partially demarcated the German-Polish border (along the Oder–Neisse line).