The lake's emerald hue is caused by light reflecting off the grassy vegetation and stones at the bottom through the transparent, nutrient-poor meltwater.
Until 2016, the lake was a world-renowned destination for scuba divers who could explore the submerged park infrastructure.
The water source is exclusively snowmelt from the surrounding Hochschwab peaks, which filter through limestone rock before entering the basin.
The lake basin serves as a grazing pasture for livestock during the autumn and winter months when the water recedes.
Grüner See, located near Tragöß, is a karst lake famous for its seasonal depth fluctuations driven by snowmelt from the Hochschwab mountain range. In spring and early summer, melting mountain snow fills the basin with crystal-clear, emerald-green water, submerging surrounding hiking trails, benches, and bridges. The lake reaches its maximum depth between May and June, typically ranging from 4 to 12 meters depending on snowpack levels. As summer progresses, the water level recedes significantly, often leaving the lake bed almost dry by late autumn. The water temperature remains consistently cold, usually between 4 and 8 degrees Celsius. The basin is fed by subterranean karst springs, contributing to its extreme water clarity and distinctive coloration. Due to environmental protection measures, all water-based activities, including swimming, diving, and boating, are strictly prohibited to preserve the ecosystem. The site is located within a protected landscape area, necessitating strict adherence to marked paths.
The elevated wooden bridge crossing a section of the lake, offering a panoramic view of the mountains reflected in the water.
Wear sturdy, waterproof hiking boots, as trails can be muddy or partially flooded even during low-water periods.
Check local water level reports before visiting to determine if the basin is currently filled or dry.
Bring binoculars to spot chamois and other wildlife on the steep slopes of the Hochschwab mountains.
Do not attempt to swim or enter the water, as rangers strictly enforce conservation laws; avoid visiting during peak weekends to escape high foot traffic.
The lake is a natural phenomenon; it is deepest in late spring and early summer and may be nearly empty in late autumn and winter.
Swimming, diving, and any water entry are strictly prohibited; stay on marked paths to protect the sensitive flora.
