Sirňák

Sirňák is a small but geologically remarkable nature reserve on the northeastern foot of Podhorní vrch, less than 3 km north of the village of Ovesné Kladruby, within the Slavkovský les Protected Landscape Area in western Bohemia. Protected since 1986, the site covers only 3.2 hectares, yet it ranks among the more unusual natural features in the Czech Republic.

What makes this site unusual?

Sirňák sits in the floodplain of the Teplá River, in a spot where sulfuric-carbonic gases seep up from underground. These emissions create the site's signature feature: bubbling mud craters formed as carbon dioxide and hydrogen sulfide escape through the waterlogged ground. Such gas vents, known as mofettes, are rare in the Czech landscape and draw the interest of geologists and naturalists alike. The peatland where they occur developed in the wet river valley and has retained its untouched, hard-to-reach character to this day.

What does the landscape look like?

The terrain is a mix of wet meadow, alder and spruce stands, and extensive peat patches. Sphagnum mosses dominate the ground cover, and the vegetation includes sundews — carnivorous plants typical of poor, acidic peatland habitats — along with ferns and other species adapted to constantly damp, difficult terrain. The combination of mineral-rich, gas-affected soil and waterlogged conditions creates a narrow ecological niche that only specialized plants can tolerate.

Is it accessible to visitors?

No road leads to the reserve. The only way in is on foot, across waterlogged and boggy ground, typically approached from the Podhorní ranger station. Given the fragile terrain and sensitive ecosystem, a visit calls for sturdy footwear and caution — this is not a site set up for casual tourism, but rather one that appeals to visitors with a specific interest in geology or botany.

Who manages the reserve?

Sirňák falls under the administration of the Slavkovský les Protected Landscape Area, which is responsible for monitoring the condition of the peatland, protecting the rare plant species found there, and ensuring that the unusual geological processes — including the gas emissions and mud craters — remain undisturbed.

Frequently asked questions

What are the mofettes seen at Sirňák? They are natural gas vents — mainly carbon dioxide and hydrogen sulfide — that bubble up through the waterlogged ground, forming the site's characteristic mud craters.

Is there a marked trail to the reserve? No, there is no road or paved trail. Reaching the site means crossing boggy, waterlogged terrain, usually from the direction of the Podhorní ranger station.

What plants grow at Sirňák? The site is known for sphagnum mosses, sundews, ferns, and other species typical of acidic, nutrient-poor peatland habitats.

Where exactly is Sirňák located? On the northeastern foot of Podhorní vrch, less than 3 km from the village of Ovesné Kladruby, within the Slavkovský les Protected Landscape Area.