Nestled among the farms and small businesses of south-central Kentucky is the community of Horse Cave, a town of about 2,250 people that was once named one of the “Most Quaint Must-Visit Small Towns in Kentucky.” People walking through downtown Main Street can find brick buildings housing florists, antique stores and family-run shops.
Beneath those quiet storefronts lies the feature the town is named for: Hidden River Cave. Today it’s known as an environmental restoration success story. For decades, though, it was considered one of the most polluted caves in the United States.
The underground river helped shape nearly every chapter of the community’s story, from early development and industry to decades of pollution that residents would eventually come to recognize by smell alone.
A simple walk down E. Main Street in Horse Cave reveals the gaping cave opening situated beside one of the town’s main roads. Passersby can look down toward the mouth of the cave and see what is known as the largest, privately operated cave in Kentucky. The cave opening sits at the bottom of a three-story sinkhole, placing the cave mouth 650 concrete steps below the street.
For Annie Holt, the cave has never just been a town feature. Holt, now the education director for the American Cave Conservation Association, grew up only a few miles away, back when Hidden River Cave was still closed, polluted, and notorious for its smell.
“The smell was horrendous, just horrendous,” Holt said. “I mean you had to hold your nose, and it wasn’t just a small thing that you would encounter walking. We would hold our nose as we drove down 31 passing through town.”
As a child, Holt and her friends called Horse Cave “Stinky Town.” Later, she learned that the odor drifting through the streets came from the cave below.
What Holt didn’t understand at the time was how long the cave had been suffering.
The collapse of an ecosystem
Major Albert Anderson purchased the land that would become Horse Cave in 1850 and plotted a town along the route to Mammoth Cave. Its location made it a regional trading center.
In 1888, Dr. George A. Thomas bought the property containing the cave’s entrance for $300, about $12,000 today, and installed a piston pump system to move water from the underground river. By 1892, he was generating electricity for his home, his dental practice and two other buildings. Horse Cave became the second town in Kentucky to have electric lighting, after Louisville.
His son, H.B. Thomas, extended that innovation into the cave itself, installing lights and launching guided tours. By 1916, visitors were descending concrete steps along a route that remains in use today.
The town’s population grew nearly 46 percent between 1920 and 1930. As development expanded, residents disposed of trash and sewage in sinkholes. The cave system drains roughly 100 square miles, meaning contaminants deposited anywhere within that area eventually enter the underground river, the town’s drinking water source.
By the mid-1930s, pollution levels had intensified. A typhoid outbreak was linked to contaminated water. In 1943, cave tours were suspended after persistent odors made conditions untenable. The city relocated its water supply to Rio Springs on the Green River, where it remains.
Industrial waste compounded the problem. A local creamery dumped excess whey into a sinkhole, introducing large quantities of nutrients into the cave’s otherwise nutrient-poor ecosystem. The imbalance triggered population surges followed by die-offs, worsening water quality.
In 1963, the town installed a sewage treatment system that relied on bacteria to break down waste. Treated effluent was discharged into dry wells that drained directly into the cave.
In 1970, a chrome plating facility began discharging chromium into the sewer system, killing the bacteria necessary for treatment. Untreated sewage flowed into the cave. In 1975, a leaking gas tank released thousands of gallons of gasoline into the waterways.
“That is really what created the greatest downfall,” Holt said.
By the 1980s, the ecosystem had collapsed to the point that few organisms survived beyond bloodworms, which tolerate low-oxygen, highly polluted environments.
In 1987, H.B. Thomas’ grandson, Bill Austin, began exploring options to restore the cave. He contacted multiple organizations and ultimately partnered with the American Cave Conservation Association, inviting the group to establish headquarters in Horse Cave and lead restoration efforts.
A modern sewage treatment facility was installed in December 1989, ending the direct discharge of sewage into the cave. Over time, water quality improved. Cave crayfish reappeared within two years. Tours resumed in 1992, and in February 2020, visitors returned to the historic tour route for the first time in decades.
Reminders of the past
In one of the offices above the lobby of Hidden River Cave, Annie Holt wears salamander earrings and slate blue hexagonal glasses. She said she has always been drawn to caves.
“I was an environmentalist, even as a child, hiking by myself out in the woods to find sinking streams and things of that nature,” Holt said.
Holt started caving when she was 16 and eventually studied geology in college. She worked in several caves throughout the region before realizing that her calling was elsewhere.
“I knew that my passion was really set in non-formal education, like the interpretation that you give in caves to the general public,” Holt said.
Holt carries a physical reminder daily of the remnants of the cave’s pollution: her mother’s engagement ring.
Her father worked at the chrome plating company that abused the Horse Cave sewer system. Holt clarified that the workers did not know what the company was doing. Holt’s father wanted to propose to her mother, but he had nothing. So one night, he stayed late at work.
He took a hardware nut and ground down all of the edges except for one. He did his best to smooth out the threads, and he dipped it in chrome. That was the ring that he proposed with. Holt now owns that ring because it no longer fits her mother.
“I wear it everyday because it not only reminds me of where my family started, of how my family started and the passion that my daddy had,” Holt said. “But this is the chrome. This is the chrome that destroyed this cave, and it is a reminder to me that even if the day is a bad day, it reminds me of why I’m here, of what happened and what I never want to see happen again.”
The work continues
Restoration efforts conducted in the cave are gaining traction on a national level. The New York Times published a story about the cave as a part of their “50 States, 50 Fixes” series in August, but the work in Hidden River Cave isn’t over.
Western Kentucky University graduate student Monica Galvez is studying sediment transport in the cave for her master’s thesis. Hidden River Cave is prone to flooding, and sediment can easily be displaced during those events. When sediment is transported, any contaminants or pollution moves with it, which makes it harder to track the source of the contamination.
The first time that Galvez entered Hidden River Cave was during a karst field studies class, the class that inspired her to pursue her master’s, but the trip was interrupted.
“It was starting to rain, and it (the cave) floods fast,” Galvez said. “So we went down to the entrance, and we walked down a little bit, but we didn’t even make it to Sunset Dome because the water was coming up.”
One of the reasons that Galvez chose to conduct her thesis on Hidden River Cave was its intense hydrologic response to flooding. The cave experienced its highest recorded amount of flooding in April earlier this year. After intense rainfall on April 6, the underground river that flows through Hidden River Cave had risen over 100 feet above its normal level. The cave experiences flooding relatively often due to it being a key drainage vessel for over 100 square miles.
The cave used to be “one of the most polluted caves in the United States,” according to the Hidden River Cave website, and now, it is known as an environmental success story. While the cave is immensely less polluted than it once was, Galvez believes the work is never done.
Upstream from the cave, there’s an industrial park, which has had its fair share of leaks over time. Galvez recalled a time she was exploring the cave, and she could see evidence of such pollution.
“Last time I was there, there was some dark, kind of hydrocarbon type substance in the sediment,” Galvez said. “And then we’re stepping through there, and as we’re stepping through, we’re stirring up the mud and releasing the gasses.”
The CO2 level in the cave rose as a result of the pollution in the water being disturbed. Galvez began to experience a headache and shortness of breath. Before this, she said she had never experienced CO2 poisoning before, but she believes that’s what happened that day.
“I’ve heard of people getting sick in there, but I hadn’t experienced it myself yet,” Galvez said.
While Galvez focuses on studying and exploring the cave, Holt’s focus lies in the education of the nearly 25,000 guests that visit annually. Hidden River Cave has also provided educational events and opportunities to over 400,000 students, teachers and various other groups. Holt and the other guides pride themselves on translating the cave’s complex history into stories visitors can understand. She hopes that this information will inspire visitors to become advocates.
“We want them to go home and go ‘what’s happening in my community that is similar, or could face the same issues, and how can I be a part of preventing it or remediating it?’” Holt said. “We want to inspire them.”
No matter how much progress is made, Holt understands how vitally important it is to remember the past and what led to the extensive pollution of the cave.
“I think the history of that cave and how that contamination really built, that’s something that we can’t forget, no matter how far away from that we go,” Holt said. “We cannot forget that.”
Outside the cave entrance today, no smell floats through the air. Tours once again run beneath the town. The stench may be just a memory now, but the lesson of the cave still remains.
