The Nysa Kłodzka (German: Glatzer Neiße, Czech: Kladská Nisa) or Eastern Neisse is a river in southwestern Poland, a left tributary of the Oder, with a length of 182 km (21st longest) and a basin area of 4,566 km² (3,744 in Poland).
Before 1945 the area was part of Germany. During the Yalta Conference it was discussed by the Western Allies as one possible line of the western Polish border. Attempts were made to negotiate a compromise with the Soviets on the new Polish-German frontier; it was suggested that the Nysa Kłodzka be made the line of demarcation. This would have meant that (East) Germany could have retained approximately half of Silesia, including most of Breslau. However the Soviets rejected the suggestion at the Potsdam Conference and insisted that the southern boundary between Germany and Poland be drawn further west, at the Lusatian Neisse.
Nysa Kłodzka originates in the Śnieżnik mountain range of the Sudetes, near the border with the Czech Republic. It is partially regulated. The river has often left its banks and flooded nearby cities, at times destroying them completely. City chronicles from Kłodzko mention floods in the following years: