Sulm, River, Styria, 83 km long tributary of the River Mur; its sources, the Schwarze Sulm and the Weisse Sulm, merge at Prarath (alt. 304 m); approx. half-way down the river lies the municipality of Gleinstaetten (alt. 308 m). The River Sulm is joined by the River Saggau ( Saggau Valley) at Grossklein (alt. 321 m) and by the River Lassnitz near Leibnitz (alt. 274 m). At Leibnitz the River Sulm has an average flow rate of 16.3 m3/sec. Close to Seggauberg (alt. 366 m) lies the small Sulm-See lake; the River Sulm flows into the River Mur near Retznai (alt. 261 m). Between Sulm and Lassnitz lie the Sausal Hills (viniculture).