The most important river course is Râul Mare, with an annual average flow of 12.9 cubic metres per second (460 cu ft/s).

The biggest threat for the park's flora (especially the one found on the alpine fields), is overgrazing, as there are numerous herds of sheep.

There are favorable conditions here for some of Europe's biggest predators to survive: the gray wolf, brown bear and the Eurasian lynx; some big herbivores like the chamois, red deer, and the roe deer, while small carnivores such as the wildcat and the European otter can also be found.

In 1973, 20 alpine marmots, brought from the Austrian Alps, were introduced in the park and released in the Gemenele glacier lake caldera.

Studies are now being performed to check if they are responsible for the decline in amphibian population through these lakes, observed during the last years.

A subspecies of the smooth newt (L. vulgaris ampelensis), endemic to the Carpathian Mountains, lives here, while the European common frog can be found all over the park.

Although very few common European viper bites were reported, tourists and villagers often kill them on sight.

Although there are several points of entry into the Retezat Mountains from the towns of Vulcan, Lupeni, Uricani, Câmpul lui Neag, and points in between, direct access to the National Park begins in the Cheile Buții area (approximately 35 kilometres (22 mi) west of Petroșani) and extends west to Câmpușel.

Almost all the villages along the highway, from Ohaba de sub Piatră, just outside Hațeg, to Merișor, just outside Petroșani, have access roads that run south into the Retezat Mountains.