The Stará řeka NNR was declared in 1956 in the parish of Holičky in the Třeboňsko PLA and the Jihočeský kraj – South Bohemian Region on a territory of 745 ha. The subject of the protection is the original channel of the Lužnice river and the surrounding alluvial plains. The river is of a natural character with many meanders, riverbank subsidences, sandbanks, permanent and periodic pools and oxbow lakes. A number of fragments of hardwood alluvial forest can be found here as well as other types of natural and cultural forests. A 4 km section of the Nová řeka canal bank with numerous old oak trees and part of the inundation zone of the Nová řeka canal with extensive marshes and two fishponds are also included in the NNR territory.
Unlike most nature reserves, this area does not protect a natural landscape with minimal human interference. On the contrary this is a territory which has been formed and shaped by human activity since medieval times, an artificial landscape which formed in place of the original marshy forests on the Lužnice alluvial plain.
The most valuable forest communities with many rare plant species are predominantly waterlogged, marshy alder carrs. In the spring we can admire the large carpets of flowering marsh marigold (Caltha palustris) and spring snowflake (Leucojum vernum) and later in the year extensive growths of bog arum (Calla palustris).
In the southern section of the reserve remnants of another valuable forest community – deciduous riverine alluvial stands with open primeval stands of massive pendunculate oaks (Quercus robur) can be found. The white bird’s-nest fungus (Crucibulum laeve) grows on remnants of dead and dying wood.
Many rare plant species occur in the oxbow lakes, open pools and lagoons or on their banks, including water violet (Hottonia palustris), the prostrate false pimpernel (Lindernia procumbens), yellow iris (Iris pseudacorus), yellow water lily (Nuphar lutea) and the white water lily Nymphaea candida.
Among the most valuable invertebrates in the NNR are beetles such as great Capricorn beetle (Cerambyx cerdo) and the hermit beetle Osmoderma eremita which are bound to the old oak stands. In the extensive growths of meadowsweet (Filipendula ulmaria) we can see the abundant Hungarian glider butterfly (Neptis rivularis). Other butterflies which live here include purple emporer (Apatura iris) and poplar admiral (Limenitis populi). The water spider (Dolomedes fimbriatus)is relatively common in the wetland biotopes. The Nová řeka flood plains are an attractive migration stopover for hundreds of migrating water birds during periods of high water and some of these birds also feed and nest here. Nesting bird species in the marshes include water rail (Rallus aquaticus), spotted crake (Porzana porzana) and snipe (Gallinago gallinago).
The kingfisher (Alcedo atthis) nests in the vertical banks of the Stará řeka. Many forest species of birds and mammals inhabit the extensive forest complexes. The black stork (Ciconia nigra), white-tailed eagle (Haliaeetus albicilla) and goshawk (Accipiter gentilis) all nest here. The reserve is a population centre for the otter (Lutra lutra).
Stará řeka NNR neighbours onto two other valuable localities, the Meandry Lužnice and Novořecké močály Nature Reserves. A proposal to join them together into a unified reserve is currently being prepared. Stará řeka NNR is accessible for visitors on several marked tourist trails. Both of the main watercourses, the Stará řeka and Nová řeka, are popular with canoeists.