The case for Champ: Sonar, sound, and our ancient sea

By Timothy Page

If you live near the lake, you already know the Champ story — the sightings going back centuries, the 1977 Mansi photo, the strange wakes off St. Albans and Port Henry. Here’s the theory that fits the evidence best: Champ is an undocumented species of small, freshwater dolphin or porpoise, living in the deeper parts of Lake Champlain. It’s not just the most exciting explanation. It’s the one that best matches the lake’s geology, its sonar history, and — above all — what’s actually been recorded on hydrophones. Here’s the case.

The Lake Used to Be a Sea

Any theory about a cetacean in the lake needs to explain how it got there. Lake Champlain’s own geology answers that question. About 13,000 years ago, the weight of retreating glaciers had pressed the Champlain Valley down below sea level. When the ice melted, seawater rushed in and formed the Champlain Sea — a real arm of the Atlantic Ocean, home to actual beluga whales, harbor seals, and walruses. We know this for a fact because of the fossils. The “Charlotte whale,” a beluga skeleton dug up in Charlotte, Vermont in 1849, still sits on display at UVM’s Perkins Museum of Geology today. It’s Vermont’s official state marine fossil.

The lake didn’t turn fresh overnight. As the land slowly rose back up — a process called isostatic rebound — the connection to the ocean gradually closed off. Saltwater got flushed out and replaced by fresh water draining in from rivers and melting glaciers. That change happened roughly 10,000 to 10,500 years ago, and it took a few thousand years, not a single season. That’s plenty of time — on an evolutionary timescale — for animals already living there to adapt to the changing water, rather than needing to swim away before it happened.

This gives the cetacean theory something most “monster” theories don’t have: real, undisputed proof that marine mammals lived in this exact water, right up until it turned fresh. The real question is whether any of them stuck around and adapted. And there’s a strong, well-documented example of exactly that happening somewhere else.

It’s Happened Before: Seals Trapped by the Same Kind of Event

The best comparison is the Saimaa ringed seal of Finland, and the parallel is striking. Around the same time as the Champlain Sea, the Baltic region went through a nearly identical process. As an old sea there drained and freshened, groups of ringed seals got trapped in what are now landlocked lakes, cut off as the land rose beneath them. One of those groups, isolated in Finland’s Lake Saimaa for roughly 9,000 to 9,500 years, is now its own recognized subspecies. New genetic research even suggests it may deserve to be called its own full species. A related group, trapped the same way, still lives in Russia’s Lake Ladoga. Both have visibly adapted to freshwater life — over a timeframe similar to how old Lake Champlain itself is.

This kind of thing happened again and again after the glaciers retreated: land rising, seas turning into lakes, and marine animals getting trapped inside them. The ones that survived did it by adjusting to the changing water — sometimes in just a few thousand years, which is fast, but well documented (Kunnasranta et al., 2021)¹. We already know seals and beluga whales lived in the Champlain basin while it was still connected to the ocean. The Saimaa seals prove that when animals get trapped like this, surviving and adapting isn’t just possible — it’s happened before, more than once. The open question for Lake Champlain isn’t whether this could happen. It’s whether it did, and just hasn’t been confirmed yet.

The Best Candidate: The Harbor Porpoise

If something did survive in Lake Champlain, the fossils point to a specific likely candidate: the harbor porpoise (Phocoena phocoena). Belugas make up most of the whale fossils found from the Champlain Sea — about 80% of them. But belugas don’t have a dorsal fin, and they don’t swim in the long, arching, multi-hump pattern that people describe seeing.

Harbor porpoises are different. They’re also found in the same fossil beds, alongside humpback, fin, and bowhead whales (Harington, 1977; Harington & Occhietti, 1988)³. And they’re a much better visual match for a “sea serpent” sighting. Most of the time, a harbor porpoise barely breaks the surface — just a quiet roll that shows the fin and a bit of back. But they can also leap and splash dramatically, especially males chasing females during mating. A small group surfacing close together, one after another, could easily look — from a distance, in low light — like one long, humped body. In addition, they are sighted and documented to this day in the St. Lawrence, the key link between the Atlantic and the .

Bigger, more dramatic “porpoising” animals like bottlenose or spinner dolphins would make an even better match visually, but none of them have ever been found in Champlain Sea fossils. They’re warm-water, deep-ocean animals that had no reason to swim into a cold, ice-filled inland sea.

The harbor porpoise is the only animal on this list that checks both boxes: it was actually here, and it could plausibly produce what people are describing.

What’s Actually Been Heard

If Champ is a real animal and not just a wave or a fish, sound is probably the best evidence we have, because echolocation is hard to fake or misread. Dolphins and porpoises make short, high-pitched click trains to navigate and hunt, along with lower whistles to communicate. That kind of layered, patterned sound isn’t something sturgeon, otters, birds, boat engines, or cracking ice reliably make. So when people on Lake Champlain report hearing exactly that combination, it’s a real clue.

The clearest case came in 2003. Researchers from the Fauna Communications Research Institute, working with a Discovery Channel crew, put recording equipment in the lake and picked up a sharp ticking and chirping sound. They said it sounded like a beluga whale or a dolphin — animals that aren’t supposed to live in Lake Champlain at all. The finding was even written up for the scientific literature; the researchers concluded the sound was likely a form of echolocation, even though none of the lake’s known animals can echolocate (Von Muggenthaler, Gregory, & Mardis, 2010)². That matters. This isn’t just a story someone told — it’s a peer-reviewed recording, even if no one’s ever matched it to an actual animal.

And it wasn’t a one-time thing. Over the years, fishing guides and boaters have reported hearing or recording clicking, chirping, and whistling sounds through hydrophones and boat equipment, mostly in the deeper stretch of lake between Port Henry and Westport. On July 31, 2014, Champ Search researchers Dennis Hall and Katy Elizabeth picked up a pulsing, low sound on their hydrophone, recorded at a spot chosen because it’s a known sighting hotspot. Elizabeth says the sound didn’t match anything in her thousands of hours recording the lake’s fish or man-made noise. Different people, different years, different equipment — all picking up the same kind of sound in the same stretch of lake. That’s a pattern, not a coincidence.

The Sonar Backs It Up

The sound evidence gets stronger once you line it up with the lake’s sonar history. In September 1993, a Japanese TV crew came to Lake Champlain and, working with local researcher Dennis Hall, hired 15 boats to sweep the lake with cameras and sonar. They picked up a large, solid object, roughly 20 feet long, passing under one of the boats. Champ Search has kept catching similar things since — in 2022, the group released sonar video of a roughly 20-foot object with what looked like a flipper moving it through the water. And in August 2024, director Katy Elizabeth recorded two more sonar contacts near the Moriah-Westport town line — moving objects about 145 feet down, too deep to be floating debris, in the same stretch of lake where the sound recordings have clustered.

This is exactly what you’d expect to find if a small group of dolphins or porpoises lived here: sonar picking up their solid bodies moving through the water, and hydrophones separately picking up the clicks and whistles those same animals would make while hunting in dark, murky water — the kind of conditions where echolocation matters most. A lot of the sightings and sonar hits come in pairs — two humps, two moving shapes, animals seeming to travel together. That fits social animals like porpoises far better than it fits a single “monster.” Independent teams, using different gear, thirty years apart, keep landing on the same basic picture: something solid, about 20 feet long, swimming deep, and making sound. That’s hard to write off as coincidence.

Answering the Objections

The biggest problem for this theory is simple: nobody’s ever found a body. No bone, no carcass, no tissue sample. That’s a real gap, but it’s less damning than it sounds. The Yangtze river dolphin went undescribed by science for years even though local fishing communities knew it well. Small, elusive populations of aquatic animals are genuinely hard to catch, even with modern tools. And nobody has actually run a dedicated environmental DNA (eDNA) test on Lake Champlain looking specifically for cetacean DNA. eDNA testing is cheap and reliable now — it’s been used elsewhere, including in Loch Ness’s 2018 survey, which found no reptile DNA but also couldn’t identify about 20% of the genetic material it collected. So the lack of DNA evidence in Lake Champlain may just mean nobody’s properly looked yet.

Skeptics also point to simpler explanations for individual sightings: lake sturgeon (which can grow past six feet and have a rolling, humped shape), otters swimming in a line, floating logs, standing waves, or boat wakes seen from far away. Those probably do explain some of the older sightings. But they don’t explain the sound and sonar evidence nearly as well as the cetacean theory does. Sturgeon don’t echolocate. And the classic “it was just a school of fish” explanation for multi-hump sightings works just as well for a small pod of porpoises surfacing together — so it doesn’t actually favor the boring explanation over the exciting one.

Where the Case Stands

Put it all together: real proof that marine mammals lived in this exact basin, a peer-reviewed sound recording from 2003, more than a decade of matching hydrophone and eyewitness reports, and repeated sonar hits over thirty years all showing the same solid, 20-foot, deep-swimming shape. No single piece of this proves a new species exists. But taken together — different researchers, different decades, different equipment, all landing on the same basic picture — this is exactly the kind of pattern that would normally justify a serious, well-funded follow-up study, not a shrug.

What’s still missing is the one thing that would turn a strong theory into a confirmed discovery: a bone, a body, or a clean DNA sample. Given how much of the sound and sonar evidence already lines up, that gap probably says more about how hard it is to catch a fast, wary animal in a deep, murky lake than it does about whether the animal is really there. Until someone runs a proper eDNA survey or sets up a long-term hydrophone array, an undocumented freshwater cetacean remains the theory that best explains everything we’ve heard, seen, and dug up so far.

Additional References

1. Kunnasranta, M., Niemi, M., & Auttila, M. (2021). Sealed in a lake—Biology and conservation of the endangered Saimaa ringed seal: A review. Biological Conservation, 253, 108908. https://doi.org/10.1016/j.biocon.2020.108908
   
2. Von Muggenthaler, E., Gregory, J., & Mardis, S. H. (2010). Echolocation in a fresh water lake. The Journal of the Acoustical Society of America, 127(3), 1862. https://doi.org/10.1121/1.3384449
   
3. Harington, C. R. (1977). Marine mammals in the Champlain Sea and the Great Lakes. Annals of the New York Academy of Sciences, 288, 508–537. https://doi.org/10.1111/j.1749-6632.1977.tb33632.x; Harington, C. R., & Occhietti, S. (1988). Inventaire complet des vertébrés marins de la Mer de Champlain (fin du Wisconsinien) et de ses voies d’accès. Géographie physique et Quaternaire, 42(1), 45–64.