Owing to the abundance of water and moisture in its territory, Rila National Park is a veritable moss kingdom. A total of 282 moss species of all ecological groups have been identified thus far, representing as much as 41% of the Bulgarian moss flora and a whopping 62% of the moss families known in this country! Though mosses are sometimes exceedingly difficult to tell apart, experts have figured out that 42 species are of conservation significanceThe cold, clear waters of high mountain lake guard a wealth of tiny algae-130 species in all-that are invisible to the naked eye.
Rila National Park's fauna is extremely rich, comprising 2,934 species of invertebrate organisms and 172 species of vertebrates, most of which form numerous, healthy, and viable populations.
Five species of fish, 20 species of amphibians and reptiles, 48 species of mammals, and 99 species of birds represent the vertebrate fauna. Twenty-four of these vertebrate species are listed in the World Red Data Book as nearly extinct.
The Park contains the largest Bulgarian populations of Balkan chamois, capercaillie, hazel hens and rock partridges, Tengmalm's owls and little owls, and martens, as well as the largest high mountain population of the souslik.
Rila National Park has some of the healthiest and most viable populations of predatory birds in Europe. The Park is also home to a group of birds characteristic of the high mountain zone: wall creeper, alpine chough, and alpine accentor, globally representing this region for the ornithofauna of the alpine biome.