Nadiža is a mountain stream near the town of Kranjska Gora, in the far northwestern corner of Slovenia. Springing from a bare rockface on the eastern slope of the mountain Zadnja Ponca above the valley of Tamar in the Julian Alps, it is the first source of the river Sava Dolinka, the longer of the two sources of the Sava, the longest Slovene river at 221 km and a tributary of the Danube.
The source of Nadiža is near the Tamar Mountain Home; immediately after emerging, the water cascades down the cliff face in a 10-m waterfall, near which the municipality of Kranjska Gora draws its water. The creek's surface course is only about 300 m long, though it flows far further underground after disappearing at the gravelly Ledine basin near Rateče. Nadiža re-emerges through the porous bottom of a two-m deep lake called Zelenci, a marshy wetland with an extraordinarily rich ecosystem, which is regarded as the permanent source of the Sava Dolinka.