Schwarza, River, Lower Austria, along with the River Pitten headstream of the River Leitha, 60 km long. Originates in the Lower Austrian Limestone Alps (near Tiefental), formed by the confluence of the rivers Duerre Schwarza and Gruene Schwarza, flows through the Hoellental Gorge which is flanked by the Schneeberg and Rax Mountains, passes Ternitz (alt. 398 m) and Neunkirchen (alt. 371 m) in the Vienna Basin and, joining the River Pitten near Lanzenkirchen (alt. 302 m), forms the River Leitha; average discharge rate is 2.4 m3/sec. at Loipersbach gauging station; generally poor water quality.