The endangered Hay’s Spring amphipod. (National Museum of Natural History)

Beneath the ground in a handful of locations in Rock Creek Park, not far from the swirl of an oblivious capital, lurks the District’s lone endangered species: the mysterious Hay’s Spring amphipod.

Fully grown, they’re about one centimeter long. They live under wet, dead leaves. They are milky white, sightless and shy. They are not photogenic.

“They look like tiny dead shrimp,” said David Culver, an environmental science professor at American University who studies amphipods.

Though Stygobromus hayi, as the endangered amphipod is affectionately known, lacks the majesty of other endangered species, such as the blue whale or Asian elephant, it is the star of a scientific paper published this summer. The amphipod’s elusive qualities made it an ideal subject for study through environmental DNA, a technique for examining microbes in soil to locate very tiny critters.

Environmental DNA, or “eDNA,” are little bits of ourselves we living creatures constantly emit into the world around us — strands of hair left on a comb, for example, or skin cells shed onto a computer keyboard.

Not wishing to exterminate members of such a celebrated endangered species, scientists screened water samples from 10 seepage springs in Rock Creek Park — not rushing rivers, but wet spots where groundwater rises to the surface — looking for bits of Stygobromus hayi. They detected the creature at four springs, including one near the U.S. Park Police Station on Beach Drive, where the animal wasn’t found with traditional methods.

“This study is the first to our knowledge to successfully employ an eDNA approach to detect rare or threatened invertebrates from subterranean ecosystems,” the study said, calling eDNA “a considerably less invasive sampling technique.”

The authors of the case study, published in the scientific journal Conservation Genetics Resources, thought it would be easier to find traces of amphipods where they hang out than actually finding the animals themselves.

Studying endangered species, after all, isn’t easy — especially a species like the Hay’s Spring amphipod. Truth be told, this unique animal, which lives on four square kilometers of Planet Earth, looks a heck of a lot like other amphipods. So much, in fact, that confirming an identification involves some unseemliness.

“The only way to find out is to kill them,” said Daniel Fong, an American University professor and co-author of the study.

The Hay’s Spring amphipod was discovered in 1938 on property belonging to the National Zoo, said Meagan Racey, a spokeswoman for the U.S. Fish and Wildlife Service. They were found at additional sites along Rock Creek in subsequent decades and act as metaphorical canaries in the coal mine.

As Washington’s recent record-setting deluge showed, storm water can be a big problem in a densely populated city. Runoff from roads can contain heavy metals that degrade the quality of soil in Rock Creek Park, especially when spewed from antiquated pipes.

All that nasty stuff in the water can kill amphipods. Indeed, the creatures helped spur a $1 million program to control storm-water runoff near the Carter Barron Amphitheatre. If they persist, that means efforts to keep pollution out of the park may be succeeding.

“They’re very sensitive to water quality,” Racey said. “The fact that they exist here is good news.”

The Hay’s Spring amphipod also grabs more headlines than the average minuscule crustacean. Activists seeking to stop construction of the Purple Line cited it as a reason not to build the line. It was also declared the District’s “official amphipod” earlier this year by Mayor Muriel E. Bowser (D).

That said, there’s a lot researchers don’t know about the Hay’s Spring amphipods. Was this eDNA from one animal or 100? Was the DNA present because an animal molted or because it died?

From here, the depths of the Earth are the limit.

“This study was more a proof of concept that we can actually detect a small, little invertebrate species,” said Matthew L. Niemiller, an ecologist at the University of Illinois at Urbana-Champaign and the study’s lead author.

“The fact that we can detect a small species like this, we can apply to other species around the world that are rare and endangered.”