Zelenci Springs is a nature reserve near the town of Kranjska Gora, in the far northwestern corner of Slovenia. It is the source of the Sava Dolinka River, a tributary of the Danube.At Zelenci Springs, water from underground Nadiža Creek (originating in the Planica Valley) re-emerges through the porous bottom of a 2 m deep lake, whose waters are noted for their deep, brilliant green. The spring and its surrounding area are named after this colour (Zelenci is a deadjectival plural noun from Slovene zelen 'green'.)GeologyThe Upper Sava Valley is the result of action by the Planica Glacier, creeping from below Mount Jalovec, the Ponce Range, and Mount Mojstrovka. The area contains many lake sediments, suggesting that Zelenci Springs is a remnant of the once much larger Lake Koren, created by the retreat of the glacier, which carried along much debris. In retreat, the bulk of it was deposited at what is now Podkoren, damming the Sava with the Koren Pass, which hemmed in glacial melt and formed an extensive lake. The Sava then tunneled through this natural dam, lowering the water level of Lake Koren until only Zelenci Springs and its surrounding wetlands were left.