The Lusatian Neisse (Czech: Lužická Nisa; German: Lausitzer Neiße; Polish: Nysa Łużycka; Sorbian: Łužiska Nysa) is a 252 km (157 mi) long river in Central Europe. It has its source in the Jizera Mountains near Nová Ves nad Nisou, Czech Republic, reaching the tripoint with Poland and Germany at Zittau after 54 km (34 mi), and later forming the Polish-German border for a length of 198 km (123 mi). The Lusatian Neisse is a left-bank tributary of the Oder river, into which it flows between Neißemünde-Ratzdorf and Kosarzyn north of the towns of Guben and Gubin.
According to the 1945 Potsdam Agreement in the aftermath of World War II, the river became part of the Polish western border with Germany (the Oder-Neisse line). Being the longest and most notable of the three rivers named Neisse (Neiße) (German) or Nysa (Polish) (the two other rivers being Nysa Kłodzka (Glatzer Neisse) and Nysa Szalona (Wütende Neiße or Jauersche Neiße)), it is simply referred to as the Nysa or Neisse. An older Polish variant, no longer used, was Nissa.
Read more about Lusatian Neisse: Name, Cities, Tributaries