Brouskův mlýn (Brousek’s Mill) NNR was declared in 1991 on an extensive area of the Stropnice river alluvial plain and covers an area of 138.20 ha. The protected area lies close to the village of Třebeč in the Jihočeský kraj – South Bohemian Region. The subject of the protection is and extensive complex of valuable aquatic, wetland and meadow vegetation communities with the occurrence of many rare and endangered plant species. The area provides nesting and feeding biotopes for wetland birds as well as abundant populations of amphibians, molluscs and wetland insects. The actively meandering channel of the Stropnice river is exceptionally well preserved. Brouskův mlýn NNR is a part of the proposed Stropnice Site of Community Importance.
The NNR territory lies in the so-called Stropnice graben in the south-western part of the Třeboň basin and consists of the lowland meandering channel of the Stropnice river at elevations of 466 – 455 metres. The rock basement is mostly formed of silimanite-biotite paragneiss of the Moldanubic unit. The Stropnice graben is filled with strata of Upper Cretaceous sandstones, conglomerates and claystones between 70 and 250 metres in thickness. The present Stropnice alluvial plain is underlain by fluvial sediments (Quaternary sands and gravels), which contain rich aquifers which draw water from the central depression and emerge on the surface as spring resurgences on the edge of the territory. The NNR lies in a mildly warm climatic zone with around 30 ‘summer’ days (above 25 °C) per year.
The vegetation cover in the reserve is formed of a complex mosaic of 10 – 12 types of aquatic, wetland, peaty and meadow communities. Currently growths of reed sweetgrass (Glycerietum maximae association) predominate with tall sedge communities (Caricetum gracilis) in places. Towards the edge of the alluvial plain these growths transform into peaty communities - Caricion fuscae alliance and moorgrass meadows – Molinion alliance. A small area of cultural forest with Scots pine (Pinus sylvestris) is included on the NNR territory on the edge of the alluvial plain. A whole range of interesting plant species grow on the NNR territory and include devilsbit scabious (Succisa pratensis), the ragwort Tephroseris crispa, Siberian iris (Iris sibirica), Nordstedt’s dandelion (Taraxacum nordstedtii), grass of Parnassus (Parnassia palustris), broad-leaved cottongrass (Eriophorum latifolium), Alpine deergrass (Trichophorum alpinum), lesser bladderwort (Utricularia minor) and round-leaved sundew (Drosera rotundifolia).
The territory has a very rich population of many dragonflies, including the skimmer Orthetrum albistylum. Many hygrophilous species of beetles, flies and spiders also live here. The rare butterflies false heath fritillary (Melitaea diamina) and scarce large blue (Maculinea telejus) live here as does the more common small pearl-bordered fritillary (Boloria selene). On the alluvial plain and in the pools we can find the common tree-frog (Hyla arborea), European fire-bellied toad (Bombina bombina), moor frog (Rana arvalis) and a large population of grass snakes (Natrix natrix). The adder (Vipera berus) lives in the forested section. The most common bird species are reed bunting (Emberiza schoeniclus) and grasshopper warbler (Locustella naevia). Of the many other nesting bird species we can also mention the bluethroat (Luscinia svecica), snipe (Gallinago gallinago) and water rail (Rallus aquaticus).
The alluvial plain was previously cut for animal bedding. At the end of the 1970s the Stropnice river channel was seriously silted up and the meadows began to degrade. Currently the territory is managed by regular grass cutting, cutting back opportunist tree and shrub species and renewal of the pools. The small areas of cultural Scots pine growths (40 – 120 years old) are cultivated in the standard way with the exception of bans on drainage and use of pesticides.