The Reserve protects the fragment of an immense low peat bog in the Narew valley. In 1967 it was created on the surface of 30.0 ha, east of the village Grądy Woniecko. Land reclamation around the reserve and a lack of systematic mowing peat-bog flora caused the appearance of  the birchen-alder forest in this place. Musk orchid, moor-king, low birch and Lapp willow belong to rare plants which appear on this land.