Odlezelské jezero National Nature Monument

The Odleželské jezero – Odlezly Lake NNM lies between the villages of Mladotice and Odlezly in the north of the Plzeňský kraj – Plzeň Region. The natural lake stretches out in a north-south direction in the closed valley under the western foot of the Potvorovský kopec Hill and belongs to the Žihelská pahorkatina Hilly Land. The national nature monument was first declared in 1975 on an area of 67.83 hectares and was re-declared in 1989. The surface of the lake lies at 413.3 metres above sea level and covers an area of 5.8562 hectares. The main subject of the protection is the lake which is dammed by a landslide – the youngest of its kind in the Czech Republic – and the surrounding landslide areas. The whole area is a collection of interesting morphological forms and an excellent example of the mechanisms of slope movements.
 
The dammed lake was formed by a landslide of Permo-Carboniferous sediments from the western slope of the Potvorovský kopec Hill into the valley of the Mladotický potok Stream after torrential rain on the 27th and 28th of May, 1872. The landslide was the result of long-term penetration of water into the claystone basement by way of cracks and erosion, which caused the sliding movement of a whole block of Carboniferous rocks (arkose, sandstones and conglomerates). Additional factors were the quarrying of sandstone blocks and the building of the railway line along the disturbed slopes on the left bank of the Mladotický potok Stream. The railway line was moved to the right bank after the landslide. The torrential rain in 1872 caused the entire block to slide rapidly into the valley and this formed a 300-metre-long dam across the valley and the lake formed behind this dam.
 
The lake is gradually being filled with sediments from the Mladotický and Odlezelský Streams and we can predict that these sediments will increase by around 1 metre every 10 years. The lake was around 14 metres deep in 1912 but the depth was only 7.7 metres when it was measured again in 1978. The duck mussel (Anodonta anatina) is an interesting species which lives in the lake. Aquatic plants which have been recorded around the head of the lake include Canadian waterweed (Elodea canadensis), spiny water starwort (Callitriche palustris), common duckweed (Lemna minor), curled pondweed (Potamogeton crispus), broad-leaved pondweed (Ptamogeton natans), and branched bur-reed (Sparganium erectum). The lake is currently used for fishing and other activities.
 
The landslide slopes are covered with forests with a predominance of Norway spruce, Scots pine, Austrian pine and European larch. The herb layer includes drooping tor-grass (Brachypodium pinnatum), wood horsetail (Equisetum sylvaticum), glaucous sedge (Carex flacca), hard rush (Juncus inflexus), wood club-rush (Scirpus sylvaticus) and coltsfoot (Tussilago farfara). A marked tourist trail leads through the monument.