Retezat National Park comprises the Retezat- Godeanu mountain ranges. The Retezat range extends north from the centre, and rises from between the Petrosani and Hateg tectonic hollows. The main characteristic of the Retezat Mountains is given by the presence of two big volcanic blocks that stretch out in the direction of Lapusnicul Mare and Barbat rivers: the Retezat type granodioritic massif to the North, stretching out over a length of more than 40 km and width of around 20 km and the Buta granodioritic massif, located in the south of the Lapusnic- Barbat valley corridor, which drops under the Jurassic deposits of the Retezatul Mic
A strip of crystalline schists with quartz schists, mica-schists and clorito -amphbolic schists stretches between the two blocks. Another strip of crystalline schists, adherent to the Danube area, stretches out to the Northwest of the northern granite block. The crystalline mass fuses with the eruptive intrusions. The sediments are represented by some Paleozoic and Mesozoic geological patches (especially Superior Jurassic and Inferior Cretaceous limestones), they are located on the eastern periphery of the Retezat (the Tulisa crest) and in the South- Southwest (Retezatul Mic). The crystalline of the getic layer can only be found on the northern face of the mountains, stretching further under the sediments of the Hateg and Petrosani hollows. The tectonic, lithology and morphologic conditions of the Retezat Mountains, together with the positioning of the peaks in relation to the direction of the oceanic air masses, make the massif the area with the highest humidity and drainage in the Romanian Carpathians. The average temperature of the rivers decreases proportionally with the altitude. It is around 4C at 1600 m and around 20C at 2200m . The maximum temperatures of the rivers rise in July- August (12 to 22 C) and the minimum ones in December - March (20C to 0C). The most important watercourse is Lapusnicul Mare, having an annual average flow of 12.9 m 3 /s. Waterfalls can be found on any brook within the Park. The ancient natural lakes play an important role in characterizing the hydrologic network of the Park. Their genesis was determined by the optimal conditions for the accumulation and transformation of the snow into glaciers, at altitudes higher than 1700 m, during the Superior Pleistocene era. Over 37.8% of the Romanian glacial lakes are situated within the Retezat National Park. Located at the bottom of the glacial basins, ranged in tieres, aligned, isolated or grouped in complexe patterns they represent a major attraction, not only for tourists, but also for the scientists who come to these places. The morphometric elements of the lakes oscillate within large limits, some of them breaking the national records: Bucura- the largest glacial lakes, Zanoaga- the deepest. The surface of the lakes is between 300m 2 (Stanisoara I) and 88612m 2 (Bucura) and the maximum depth is between 0 - 3 m (Stanisoara I & II) and 29 m (Zanoaga). The volume of the lakes varies between 90.3 cubic m (Galesul II) and 693.152cubic m (Zanoaga). Although they have relatively small surfaces, the glacial lakes have a highly important role in the regulating draining of the rivers in the Retezat Mountains. 58 permanent glacial lakes exist in the entire massif, located between 1700m and 2300m altitude. Some bibliographical sources mention the existence of over 80 glacial lakes.
The Flora and plant communities
Retezat is famous for its floral diversity, sheltering around 1190 superior plants species of the 3450 species known in Romania. The existence of more than a third of the Romanian flora in this area is one of the reasons for which it was declared a National Park. An approximate number of inferior species adds to the above-mentioned ones. This is the reason why the interest of the botanists in the flora of Retezat started quite early, in the second half of the 18th century. However, representative works for the area appeared later, Borza (1934), Nyarady (1958) (who published „The Flora and Vegetation of the Retezat Mountains“) and Csuros and others (1956) making a great contribution. Over 90 endemic species, of a total of 127- 400 endemic species in Romania, are extremely important to conservation of the plants in Retezat. The first endemic plant reported in RNP, was the, Ddraba dornerii, discovered in 1858 by Heuffel. The 130 rare or vulnerable plants of the „Red list of the superior plants in Romania“ (published in 1994- Oltean and others) are also of great importance.
In the second half of the 19th century, Bieltz and Csato carried out the first scientific studies on the fauna of Retezat.. During the next century, many researchers studied the fauna of the massif. Due to its very diverse habitats, Retezat National Park shelters a particularly rich fauna, in number of species and population. The invertebrates, represented by thousands of species from all the Carpathian habitatshave not been categorized, although they were much studied. The fish are represented by 11 species, Sabanajewia aurata being one of them, which is an endemic species in the Danube area. More than a half of the Romanian amphibian species totalling 11, can be found in Retezat. The specialists consider 8 of these species as rare and vulnerable, at the national level.
The reptiles in the park are represented by 9 species, almost 40% of the Romanian terrestrial reptiles. Although few cases of viper bites have been recorded, tourists and natives often kill vipers. The number of bird species in the park is large for a mountain area. There are 185 species, half of the Romanian bird species. 122 of them nest in the Park and nearby areas. Rare species like the mountain aquila, Aquila chrysaetos, (also represented on the Park logo), Lesser spotted aquila Aquila pomarina, the serpent eagle (Circaetus gallicus), the migratory falcon (Falco peregrinus), the mountain cock (Tetrao urogallus), Bubo bubo, Glaucidium paseinum, the black stork (Ciconia nigra) and other rare species can be found here. 55 species of mammals, 23% of the European terrestrial mammals, have been recorded in the Retezat National Park, proving once again the diversity of the natural habitats of this area. The Park offers survival conditions to the most important European large carnivores: the wolf (Canis lupus), bear (Ursus arctos) and lynx (Lynx lynx).
Big herbivores such as chamois (Rupicapra rupicapra), deer (Cervus elaphus) and the roedeer (Capreolus capreolus) can also be found here. The smaller carnivores, such as wildcat (Felix silvestris) and mustelines find micro mammals in the different habitats of the Park, which provides them with food. The bears use caves in Small Retezat during the winter and bats hibernate here, and also use them for shelter during summer days. There have been 13 species of bats identified in the Park: Rhinolophus ferrum-equinum, Vespertilio murinus and Pipistrelus pigmaeus. The otters Lutra lutra can be found in some of Retezat’s rivers, using the rich fish resource as food. In 1973 a team of scientists from the Romanian Academy- Commission of Natural Monuments introduced, 20 alpine marmots which originated in the Austrian Alps. The marmots were released in the Gemenele Lake basin and can now be found in all the glacial valleys and basins from under the Custurii Saddle to the Zanoaga Lake basin. The impact of this non- native species on the vegetation and soils is unknown.
According to LAW, 22 of the mammals in Retezat require strict protection, 13 are of community interest; their exploitation is a concern in the management measures, being included in Annex 5 of the Law. The rich fauna of the Retezat National Park shows once again the existence of natural habitats little affected by human activity.