The Břehyně – Pecopala NNR was declared in 1967 on an area of 903.50 ha, but had been protected since 1933 as part of a larger protected area.
The reserve is one of the most significant protected areas in the Liberecký kraj – Liberec Region and combines a wide variety of biotopes which are typical for the Dokeská pahorkatina hilly land, from the Břehyňský rybník fishpond with its accompanying reedbeds, peatbogs, wet meadows and waterlogged spruce stands to the Pecopala sandstone castellated rocks with forest stands of acidophilous and herb-rich beechwoods and pinewoods. Due to its large surface area, variety of biotopes and georelief and inaccessibility, the NNR can boast a high species diversity and is the home of many significant flora and fauna species. The reserve is also a significant nesting area for many types of birds.
The Břehyňský rybník fishpond has been included in the List of Wetlands of International Importance under the Ramsar Convention since 1991 and is a part of the Českoliposko-Dokeské pískovce a mokřady (Česká Lípa and Doksy sandpits and wetlands) SPA – Bird Area under the Natura 2000 system since 2004. In 1994 the NNR was included in the network of biogenetic reserves of the Council of Europe as one of only two territories in the Czech Republic.
A wide variety of biotopes are found on the territory of the reserve. By the Břehyňský rybník in the lower section we can find waterlogged peatbogs and fens, which pass into pinewoods on the sandstone basement and spruce stands on the peat. Alders (Anus glutinosa) are well represented, along with pendunculate oaks (Quercus robur) and silver birch (Betula pendula) in drier areas.
The vegetation on the Mlýnský vrch hill is quite different from the growths around the fishpond and at Pecopala. The dominant tree species at the top of the hill is beech (Fagus sylvatica) but towards the foot of the hill Scots pines (Pinus sylvestris) predominate with scattered alder (Alnus glutinosa), silver birch (Betula pendula) and Norway spruce (Picea abies).
The peak of Pecopala is covered with acidophilous and herb-rich beechwoods and mixed forest stands. The mixed stands include Norway spruce (Picea abies), European larch (Larix decidua) and silver fir (Abies alba). The deciduous trees here include sycamore (Acer pseudoplatanus), hornbeam (Carpinus betulus), silver birch (Betula pendula) and pendunculate oak (Quercus robur). Other trees which occur in the stands on Pecopala are Douglas fir (Pseudotsuga menziesii), Weymouth pine (Pinus strobus), ash (Fraxinus excelsior) and European aspen (Populus tremula).
The most extensive flora types in the reserve are the aquatic plant communities reedbeds on the banks of the ponds, tall sedges and peatbog communities. The most endangered communities are the peatbogs, pinewoods on the peat, wet meadows and sedges. In recent years approximately 60 endangered plant species have been recorded in the reserve, including crested buckler fern (Dryopteris cristata), fen orchid (Liparis loeselii), the early marsh orchid (Dactylorhiza incarnata subsp. serotina), the white water-lily Nymphaea candida, white beak-sedge (Rhynchospora alba), labrador tea (Ledum palustre) and creeping willow (Salix repens). Of special significance was the finding of the critically-endangered bog orchid (Hammarbya paludosa) from 1994, as this plant was previously considered extinct in the Czech Republic.
The reserve is one of the most significant wetlands in the North Bohemian region. By the end of the 20th century 164 bird species had been recorded here. The locality provides nesting sites for the bittern (Botaurus stellaris), crane (Grus grus) and white-tailed eagle (Haliaeetus albicilla). Otters (Lutra lutra) have been recorded here as well as the reptiles – adder (Vipera berus) and viviparous lizard (Zootoca vivipara). The agile frog (Rana dalmatina) lives here and the fire salamander (Salamandra salamandra) can be found in the Pec beechwoods. Stock doves (Columba oenas) nest on Pec hill and the red-breasted flycatcher (Ficedula parva) has also been observed here.
Research into mollusc populations in the NNR identified 49 species of predominantly aquatic molluscs, 41 gastropod species and 8 species of mussels.
The critically endangered crustaceans: the tadpole shrimp (Triops cancriformis) and the fairy shrimp (Branchipus schaefferi) have been recorded on the southern edge of Pecopola.