About this place
Hromnické jezírko (also known as the Red Lake, or Hromnické Červené jezírko) is a small but striking lake in western Bohemia, in the Hromnice municipality (near the village of Žichlice), not far from Plzeň in the Czech Republic. The lake formed on the site of a former slate quarry, after the mine's drainage shaft collapsed, and today it is one of the most distinctive natural landmarks in the region.
Where is Hromnické jezírko located?
The lake lies near the village of Hromnice, on the Třemošná stream, at an altitude of about 340 meters above sea level. It measures roughly 130 meters in width and 190 meters in length, with a depth reaching up to 18 meters. It occupies a depression about 60 meters below the surrounding terrain, created when the old drainage shaft of the slate mine collapsed.
Why is the water red?
The lake's most recognizable feature is its intensely red-colored water, caused by iron compounds and sulfuric acid present in it. This is why the site is commonly called the Red Lake (Červené jezírko). The water is highly acidic, with a pH of only 2.6-2.8, roughly comparable to a weak solution of sulfuric acid. Under these conditions no biological life can survive, which is why the lake is often described as "dead": it is sterile, with no aquatic flora or fauna.
What is the history behind the lake?
The site's history goes back to 1578, when slate quarrying began here to produce alum, used at the time for dyeing and bleaching textiles. From the early 19th century onward, sulfuric acid was also extracted from the slate. Mining continued until 1896, when it was abandoned after cheaper methods of producing sulfuric acid were developed in England. Once the mine closed and its drainage shaft collapsed, the pit gradually filled with water, forming the lake seen today.
Is the lake a protected area?
Yes. Because of its unique character, a nature reserve covering 12.2 hectares was established here in 1975. Hromnické jezírko is considered a unique site on a European scale and ranks among the notable tourist attractions of the Czech Republic.
Can you swim in the lake?
Given the chemical composition of the water - strong acidity and the presence of sulfuric acid - swimming here is neither advisable nor safe. Still, the site is worth visiting as a scenic viewpoint and a stop along a hiking route. Local trails connect Hromnice with nearby villages, including Žichlice and Bykov, making the lake easy to combine with a longer walk through the Plzeň region.
Frequently asked questions
Where exactly is Hromnické jezírko located? In the Hromnice municipality near Plzeň, on the Třemošná stream, at an altitude of about 340 meters above sea level, close to the village of Žichlice.
Why does the lake have a red color? Because of the high concentration of iron compounds and sulfuric acid in the water, a legacy of the former slate mine.
How deep is the lake? Its depth reaches up to 18 meters, with a surface area of roughly 130 by 190 meters.
Since when has the lake been protected? Since 1975, as a nature reserve covering 12.2 hectares.
Do fish or aquatic plants live in the lake? No - the strongly acidic, sterile water prevents any biological life from developing.
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