Velký a Malý Tisý NNR was declared (as a stated protected area) in 1957 on a territory of 615 ha within the Třeboň Basin and the Jihočeský kraj – South Bohemian Region and is among the most important fishpond reserves in Bohemia. The reserve includes a complex of 14 fishponds, of which the largest is the Velký Tisý which is officially recorded at 313 ha with a water surface of around 275 ha. The irregular banks of the Velký Tisý fishpond with many islands and peninsulas and the connection between the banks and the surrounding wet meadows and smaller water surfaces allowed the formation of exceptionally valuable wetland localities with extensive littoral growths and numerous animal and plant species.
Among the most significant protected plant species which occur on the reserve territory we can find green-winged orchid (Orchis morio), water pygmyweed (Tillaea aquatica), tufted loosestrife (Naumburgia thyrsiflora), intermediate bladderwort (Utricularia intermedia), lousewort (Pedicularis sylvatica), adderstongue (Ophioglossum vulgatum), the marsh fern (Thelypteris palustris), interrupted club-moss (Lycopodium annotinum), marsh pennywort (Hydrocotyle vulgaris), grass of Parnassus (Parnassia palustris), lesser butterfly orchid (Platanthera bifolia) and water violet (Hottonia palustris). Dozens more species are also included in the Czech Republic’s Red Book of Endangered Flora. A typical species for the littoral belts is arrowhead (Sagittaria sagittifolia).
Among the most important protected species of invertebrates on the territory we can find the hermit beetle Osmoderma eremita, the butterflies purple emporer (Apatura iris) and Hungarian glider (Neptis rivularis), and the swan mussel (Anodonta cygnea).
The most significant and most researched fauna of the Tisý fishponds are the birds. In addition to common birds species, the white-tailed eagle (Haliaeetus albicilla), marsh harrier (Circus aeruginosus), common tern (Sterna hirundo), blue throat (Luscinia svecica), water rail (Rallus aquaticus), little crake (Porzana parva), penduline tit (Remiz pendulinus), black kite (Milvus migras) and bearded tit (Panurus biarmicus) all nest on the NNR territory. The reedbeds and surrounding growths provide nesting sites for dozens of bird species which are bound to these biotopes.
The Velký Tisý fishpond is also an important stopover and gathering point for many migrating birds. At the end of the summer and in the autumn we can observe flocks of thousands of ducks and geese here. The great white egret (Egretta alba), cormorant (Phalacrocorax carbo) and many other water birds occur here.
In addition to the birds we have already mentioned, the following marsh and water birds can all be observed: pintail (Anas acuta), red-crested pochard (Netta rufina), grey heron (Ardea cinerea), bittern (Botaurus stellaris) and mute swan (Cygnus olor). In the groves we may also observe the golden oriole (Oriolus oriolus).
The most significant part of the NNR, the Velký Tisý fishpond was one of the first of the large carp breeding ponds to be built in the Třeboň basin in 1505 by the builder Štěpánek Netolický. The Zlatá stoka (Golden Canal) was built between 1506 and 1520 to supply the fishponds with water and flows around this large fishpond on the southern side. Until the 1950s the fishpond banks were used quite intensively for grazing and haymaking so woody plants were regularly cut back and removed. Together with the relatively low intensity of fish farming these factors allowed the development of rich growths of littoral vegetation. The results were extensive wetland growths merging into wet meadows and pastures. At the end of the 19th century this locality was studied mainly for its botany but ornithological research has been more intensive over the last 50 years and the reserve was first declared in 1957 for its ornithological significance. A wooden terrain station which is owned by the National Museum in Prague was built on the north bank of Velký Tisý in 1952, and provides a base and accommodation for ornithologists researching the bird life of the area.