Jankovský potok National Nature Monument

The Jankovský potok (Stream) NNM was declared in 1992 on an area of 71ha, in the kraj Vysočina - Bohemian-Moravian Highlands Region and is administered by the Blaník PLA Administration. The protected area includes the Jankovský potok Stream and its alluvial plain from its source near the village of Jankov to the hamlet of Hojkovy, which lies approximately 13km downstream. The subject of the protection is the oligotrophic (mineral-poor) communities of the water flow with the freshwater pearl mussel (Margaritifera margaritifera) and the neighbouring meadow and peatbog communities with rare and endangered plant and animal species.
Alder-ash alluvial forests and the initial stages of alder stands on former meadows can be found along the banks of the stream. Oligotrophic communities of sedge wetlands, wet and peaty meadows, alder stands and reedbeds which are rare today can still be found here as a result of the natural character of the stream and its alluvial plain. The vegetation on the wet meadows consists of sedge-moss communities of the Caricion fuscae alliance and wet thistle meadows of the Calthion alliance. Enclaves of tall sedges and fragments of transition mires have formed on waterlogged localities. Rare plant species which have been recorded here include round-leaved sundew (Drosera rotundifolia), bogbean (Menyanthes trifoliata), broad-leaved marsh orchid (Dactylorhiza majalis), lousewort (Pedicularis sylvatica), slender sedge (Carex lasiocarpa) and grass of parnassus (Parnassia palustris).
The most notable zoological aspect of the monument is the unique population of the critically endangered freshwater pearl mussel (Margaritifera margaritifera). The upper reaches of the Jankovský potok Stream represents their only known locality in the Vysočina region and one of the last localities in the Czech Republic. The freshwater pearl mussel population is so weak that it would probably not be able to recover to a position ensuring independent and long-term survival. With regard to the small size of the population, unfavourable age structure and also the disturbed reproductive capability of the individual mussels, this population cannot survive without active support, even if their habitat is improved. Forty eight-year-old pearl mussels, which were bred in isolation on the Blanice river, were introduced at suitable localities along the Jankovský stream during 2005. These introduced mussels will be systematically monitored.
The brook lamprey (Lampetra planeri), bullhead (Cottus gobio) and the broad-fingered crayfish (Astacus astacus) also occur in the stream. Alpine newts (Triturus montanus) and smooth newts (Triturus vulgaris) can also be found in and around the stream, while birds such as the snipe (Gallinago gallinago), whinchat (Saxicola rubetra) and others can be observed on the wet meadows.
The intensification of agriculture in the region over the last several decades, including increased use of fertilisers and pesticides, land drainage and increasing the proportion of arable lands has had a notably negative influence on the locality. These changes in agriculture have led to changes in the water parameters (especially an increase in the nutrient levels), changes in the pH and temperature conditions which are endangering the survival and reproduction of the freshwater pearl mussels in the stream.
Improvement of the habitat of the pearl mussels will only be possible if major changes are made to the system of cultivation in the whole Jankovský potok catchment, including on lands which lie outside the protected area.
The territory is accessible from the village of Jankov, where we can find the stream flowing through a wide alluvial plain with a complex of wetland localities and water surfaces to the west of the village. As the stream flows to the north the protected area narrows to the width of the Jankovský stream itself. We can also follow the character of the stream from roads and tracks which cross over it and on paths leading from the villages of Vyskytná, Mysletín and Zachotín.