Since earning his M.S. degree in 2023 from the UF/IFAS Department of Soil, Water, and Ecosystem Sciences (SWES), Anthony Halcyon has continued pursuing field-based exploration in unique and understudied environments. Most recently, he joined an expedition in Big Cypress National Preserve. The mission was to investigate Deep Lake. It is one of South Florida’s deepest natural lakes and a site long associated with unusual geological and ecological characteristics. This is Anthony’s account of exploring the hidden world beneath the surface of Deep Lake.
By Anthony Halcyon
When most people think of Big Cypress National Preserve, they probably picture iconic cypress domes, vast marshes, and endless stretches of subtropical wilderness that define the Everglades. Few would expect one of South Florida’s deepest natural lakes to lie hidden within such a landscape. Yet Deep Lake, a sinkhole lake within the preserve, offers exactly that. It is a place where the familiar surface of the region gives way to something stranger and far less understood. It is the perfect place for The Explorers Club to investigate.
The expedition was carried out as an independent study through the Club. The goal was to get a better understanding the lake’s unusual character. We used a remotely operated vehicle (ROV) and an autonomous underwater vehicle (AUV). These allowed the expedition team access below the lake’s surface and gather bathymetric observations. We hoped the data might help explain why Deep Lake has long stood apart from other water bodies in the region.
Wading into the Deep
One of the key figures behind the expedition was Ryan Crutchfield. He is a leader within the Florida Chapter of The Explorers Club and served as the study’s principal investigator. Ryan first came across Deep Lake while reading historical accounts and books about the region, where references to the lake and its unusual reputation stood out. He secured the permits through the National Park Service that made the fieldwork possible and later approached me about long-standing local accounts claiming that Deep Lake supports both freshwater and saltwater species.
Along with those biological observations came another intriguing possibility: that the lake could function as a halocline system. Students in UF’s SWES program may already recognize the term, but for those unfamiliar with it, a halocline occurs when layers of water with different salinity levels remain partially separated instead of mixing evenly throughout the water column. In simple terms, fresher water overlies denser, saltier water, creating a distinct boundary within the same body of water.
Using Technology to See Below the Surface
Perhaps the most unique aspect of the expedition, at least for me, was the use of modern underwater systems to investigate a place that has remained relatively obscure. Our ROV was directly operated by a human pilot, while the AUV used AI-assisted navigation and satellite-linked mission support to carry out its assignments. To my knowledge, this kind of coordinated ROV/AUV field operation remains relatively novel, and we may have been among the first teams in the United States to use the AUV in this way.
Even with advanced tools, however, fieldwork often demands improvisation. When the ROV camera began cutting in and out, we traced the issue to a failing connection point on the power tether. Like many field scientists before us, we improvised: using two sticks from the ground and a small amount of electrical tape, we built a makeshift splint around the weak point, essentially treating the cable like a broken arm. It was a simple fix—maybe a dollar’s worth of tape and two ordinary sticks—but it stabilized the problem, produced a few funny photos, and, most importantly, allowed us to continue the mission.
Near the surface and in the upper water column, we confirmed an unlikely mix of both freshwater and salt-tolerant fish, including gar, bass, tilapia, snook, and a remarkably large tarpon that could almost be mistaken for a mermaid when it surfaced. More than a few curious alligators also made appearances. The lake immediately took on a contradictory character, as though several ecological stories were unfolding within the same basin at once.
Yet it was not only the aquatic life that held my attention.
The Hidden World Below
Through underwater footage, we also caught glimpses of the lake’s walls. Because Deep Lake is a sinkhole lake, these walls were unlike anything one expects to see in a typical Florida water body. They appeared as a mesmerizing, almost alien display of karst topography, textured and sculpted in ways that felt more like the interior of submerged ruins than a natural lake margin. In some sections, we spotted fossilized sand dollars embedded directly into the rock, adding to the sense that the lake was preserving fragments of a much older world beneath the surface.
At one point, I may have fallen victim to the very human tendency to see patterns in natural formations. Certain contours in the rock resembled a hidden catacomb system tucked into the karst itself. I know it was a trick of the mind, but more than one member of the expedition commented on the “thousands of skulls” appearance, and the impression proved memorable regardless.
The deeper portions of the lake told a very different story from the surface. Conditions near the lake floor suggested a far more turbid, mineralized, and chemically distinct environment. In practical terms, turbidity refers to how cloudy or particle-rich the water is, often indicating that lower zones contain far more suspended material than the clearer upper waters.
The AUV’s bathymetric scans of Deep Lake’s sinkhole walls. (Images from The Explorers Club) Click on image for full size view.
While these observations do not conclusively demonstrate the presence of a true halocline, they do suggest that the lower portion of the lake operates under noticeably different conditions than the upper water column. More confidently, the evidence points toward the lake functioning as a chemocline—a boundary where the chemistry of the water changes significantly with depth.
Why Deep Lake Matters
Deep Lake is more than a scenic oddity. It is a natural sinkhole system within one of Florida’s most ecologically important landscapes, and that alone makes it worthy of attention. Beyond its geologic rarity, the lake may also serve as a small but revealing example of how hidden aquatic systems can preserve unusual chemistry, biological surprises, and unanswered questions even in well-studied regions.
There is also something valuable in the act of investigating such places carefully and honestly. Not every expedition results in a dramatic conclusion, and not every field measurement resolves a mystery. When I was a student at UF, I learned early on that true “Eureka!” moments are rare in science. This is especially true in exploratory science. That does not mean discoveries are absent. Instead, discoveries often lead to even more questions. Those questions lead to a stronger need to revisit sites like this for further investigation.
Sometimes the work of exploration is simply to narrow possibilities and discard assumptions. The current evidence suggests that Deep Lake is not merely a brackish basin with a clean saltwater layer. Perhaps it is something more nuanced: a sinkhole lake with a chemically and physically distinct lower zone.
The Need to Explore More
As for how saltwater fish arrived in the system in such numbers, we have a hypothesis. Integrating sonar into a follow-up expedition may help determine whether a subterranean connection to the ocean exists. Another possibility is that periodic flooding events allowed saltwater species to enter the lake.
We are also planning to reapply for permits. The idea is to expand the study to include sampling with a Van Dorn bottle sampler and a field probe. These tools would allow us to collect real-time measurements of salinity, turbidity, pH, temperature, dissolved oxygen, and other variables. Combined with sonar mapping, this may finally provide enough information to determine what is truly happening within Deep Lake.
For now, we have only informed speculation, but even that provides a compelling reason to return and continue exploring. My hope is that this expedition serves as a beginning rather than an endpoint: the first layer of context encouraging deeper and more rigorous investigation into what lies beneath the surface of this remarkable sinkhole lake.
Acknowledgements
Anthony Halcyon received his B.S. degree in Environmental Management in Agriculture and Natural Resources and his M.S. degree in Soil and Water Sciences, both from the UF/IFAS Department of Soil, Water, and Ecosystem Sciences.
The featured image of Deep Lake is from the U.S. National Park Service. Mike Loizzo edited and published this blog post.
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