Centuries ago, peasants spoke of baby dragons living deep underground. Today we know them as olms. Photograph by Charles E. Mohr / Getty

Deep inside Postojna Cave, an ancient wonder of rock and water not far from the Slovenian capital city of Ljubljana, sits a modernist aquarium—an anachronism of steel and glass and blue lighting. Seven hundred thousand people visit Postojna each year, not only to see the cave, which evokes Gaudí’s most elaborate neogothic confections, but also to observe the creatures that live in the aquarium. These are the olms, aquatic salamanders of the species Proteus anguinus, known colloquially as baby dragons. They have flat heads with a ruff of lucent pink gills, long slithery bodies, and delicate little legs. Their skin, which covers their mostly undeveloped eyes, lacks pigment, leaving their internal organs visible and giving them an eerie glow. In the course of their lives, which may last as long as a century, olms can grow to a foot in length. They are the largest cave-dwelling animals in the world, apex predators adapted to a harsh existence in the cold, subterranean dark. They can survive for a decade without eating (tiny cave shrimp make up a substantial part of their diet), and they breed only once every six or seven years.

In late January, a female olm laid an egg against the glass of the Postojna aquarium, inaugurating what might seem a disproportionate flurry of international media attention. She produced nearly sixty more eggs in the ensuing month, and has been written up everywhere from the Slovenia Times to the New York Times. “This is very cool—it is quite extraordinary,” Primož Gnezda, a biologist at Postojna, told the BBC. Some have even joked about the olm being named the Slovenian Woman of the Year. The other six olms have been moved out of the aquarium, which is now boarded up, and some of the early eggs are showing signs of fetal development—the nubs of heads and backbones.

An olm egg in the Postojna aquarium. Photograph by Iztok Medja / Postojna Cave Photograph by Iztok Medja / Postojna Cave

Why the joyful uproar? Part of the answer is that the olm is deeply embedded in the mythology of Central Europe and the Balkans. The salamander’s S-curve has been found carved into the weathered stone of at least one stećak, a type of medieval tombstone that lies scattered across the region. Its first mention in literature appeared in 1689, in the fifteen-volume encyclopedia “The Glory of the Duchy of Carniola,” by the naturalist and polymath Janez Vajkard Valvasor. A student of the Enlightenment and the first Slovenian (or, at the time, Carniolan) to be inducted into the Royal Society of London, Valvasor heard stories about baby dragons while investigating the unusual behavior of a spring near the town of Vrhnika, about fifteen miles west of Ljubljana. Each day, the spring would run strongest at around nine in the morning, then the flow would lessen; the stronger flow would resume at about midnight. The villager who showed Valvasor the spring explained that a dragon lived in the cave beneath it. When the water filled the cave, reaching the dragon’s neck, the beast would become uncomfortable and shift around, emptying the cave and disrupting the spring. Curious but skeptical, Valvasor asked the man why he thought there was a dragon. Because, the man explained, after heavy rains, baby dragons would wash up aboveground, a clear indication that an adult lived below.

Olms still get marooned at the surface after heavy rains, and dragons still hold an important place in the Slovenian national consciousness. Ljubljana’s iconic architectural feature, Zmajski Most, or Dragon Bridge, boasts four sheet-copper dragon statues, one at each corner. St. George, who is famous for his dragon-slaying, watches over the city as the patron saint of the castle chapel. Ljubljana is also where Jason and the Argonauts are said to have landed after recovering the Golden Fleece, and some versions of the story have Jason slaying a dragon in a lake between Ljubljana and Vrhnika. As the dragon became a symbol of Ljubljana, so the olm became a symbol of Slovenia’s natural heritage and national identity, even appearing on one of the coins for the tolar, the country’s pre-euro currency. During the nineteenth century, when railroads first flooded the area with tourists, the olm became a popular souvenir. Locals would capture the salamanders when they washed up aboveground and sell them in glass jars. “You hear about the olm in elementary schools,” Sašo Weldt, another biologist at Postojna, told me.

As Valvasor’s account suggests, though, the olm is representative of something more. Postojna is one of many interconnected caves in the Dinaric karst, a swath of limestone that runs along the Adriatic Coast, from northeast Italy through Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, and Albania. The rock is arid aboveground and wet below; most of the region’s drinking water comes from its vast system of aquifers. Because the olm has adapted to these subterranean conditions, which have remained relatively stable for millennia, it is a reliable bellwether of changes to the ecosystem, including those resulting from human activity such as development and pollution. “Everybody connects it with clean water,” Dušan Jelić, the president of the Croatian Institute for Biodiversity, told me. Historically, when villagers found a stranded olm, “they would return it to the dragon, because the dragon was responsible for the water.” Lose one, Jelić said, and you’ve likely lost the other.

According to Gregor Aljančič, an evolutionary biologist at the Tular Cave Laboratory, in Kranj, the olm is in decline. In 2009, it was classified as “vulnerable” on the International Union for Conservation of Nature’s list of threatened species. Aljančič explained how toxic chemicals from unregulated sewage, leaky waste-treatment plants, and agricultural pesticides have seeped into the ground and contaminated the water. High levels of pollutants such as mercury and P.C.B.s have been detected in tissue samples taken from wild olms, whose populations are retreating deeper underground as their habitat continues to be compromised. In places like Bosnia and Herzegovina, where the economy is struggling, marshalling the resources to address large-scale pollution is a profound challenge. In Croatia, huge hydroelectric engineering projects are diverting water from the ancient cave systems and dissolving the barriers that once kept ecosystems aboveground separate from those below. The isolation that has made the Dinaric karst a hot spot of subterranean life since the end of the Ice Age is breaking down.

The olm is, certainly, an animal worth celebrating. In 2012, the British naturalist David Attenborough picked it as one of ten endangered species that he would take on his personal ark. The salamander possesses an astonishing set of sensory systems, including the ability to detect both Earth’s magnetic field and the bioelectric fields of other organisms, and photosensitive skin. (Shine a flashlight on the tip of an olm’s tail and the animal will quickly slide away.) Its frilly pink gills are a telltale sign of neoteny: most amphibians lose their gills as they develop, but the olm retains its larval form, never fully developing into an adult. This has recently caught the attention of researchers studying the mechanisms of aging. But biologists may not get the chance to explore the olm’s other secrets. “We’re losing this information before we understand it,” Aljančič said.

If the olm eventually disappears, Slovenians will have to wrestle with a new national identity. They will no longer be the country of dragons but the country where the dragons died. Such moments of reckoning are going on all over the world as species falter and human activity continues to change the ecosystems that we rely on for survival. In Europe, China, and the United States, hundreds of millions of people rely on karst formations for fresh drinking water, and in many of these places a crisis of clean water is already under way. We may have built a tiny ark for a clutch of olm eggs, but the delight with which this story is being told seems to miss the point. There is danger in false assurance, and the fairy tales that we once told ourselves no longer serve, up here in the light.

Correction: An earlier version of this article mischaracterized the extent to which olms have been observed to breed in captivity and in the wild. It also suggested that neoteny may be the key to the olm’s longevity; such a link has yet to be established.