Zelenci, Nature reserve in Kranjska Gora, Slovenia.

Zelenci is a nature reserve near Kranjska Gora whose 2 m deep lake is fed by underground Nadiža Creek rising through porous chalk in tiny jets, a phenomenon found nowhere else in Slovenia. The water keeps 5 to 6 °C year-round and shows bands of turquoise and emerald green, mirroring the sky; leafless brown shrubs and green trees line the low bank.

Zelenci Springs is a remnant of the much larger Lake Koren, formed when the retreating Planica glacier left debris that dammed the Sava at today's Podkoren. The river cut through this natural dam, lowering the lake until only the springs and surrounding wetlands remained. Slovenia declared the 47-hectare site a nature reserve in 1992; the Slovene source gives 14 ha.

The name Zelenci comes from the Slovene word zelen, 'green', after the colour of the spring lake. The painter Ladislau Benesch (1845–1922) depicted the springs and their surroundings on canvas. Visitors today walk the maintained trails with informational signs, viewing bridges and an observation tower.

Visitors can explore the area via wooden pathways that allow access to the wetlands without damaging the terrain. The best time to visit is during dry weather when the walkways are easiest to navigate.

The water stays liquid even during the coldest months, a rare phenomenon linked to the temperature of underground springs. This feature keeps the area active throughout the year and allows observations not possible at many other locations.