Ottawa River Cave System

Jill Heinerth, a cave explorer and collaborator with Dr. Andre Martel, shared her experiences and findings from the Gervais Caves, a network of underwater caves in the Ottawa River. The caves, home to a diverse ecosystem including freshwater mussels, are a unique habitat with a rich history of human exploration and potential environmental concerns. Heinerth emphasized the importance of protecting this ecosystem, highlighting its ecological significance and the need for further research.

​Marie Zettler, Local Journalism Initiative Reporter, The Eganville Leader, February 19, 2025

Orginially posted to a Facebook Group (The Valley Spreader)

Dr. Andre Martel, Ph.D. Zoologist and principal investigator in a research project about freshwater
mussels, and cave explorer, author, photographer and filmmaker, Jill Heinerth, who collaborates with him, shared their experiences and findings with a Westmeath audience February 6. They work extensively in the cave network known as the Gervais Caves, under the section of the Ottawa River that loops around the “Westmeath Peninsula.” This is the conclusion of a two-part series.

Westmeath – Ms. Heinerth became part of Dr. Martel’s diving team in 2022.

“It gives me great gratification to be working in my own watershed, because I live not too far from here,” she said. “The complex, fascinating reproductive system of freshwater mussels was part of what got me pretty excited about exploring the cave itself. But the life inside the cave is far beyond just the mussels. There’s so much life in there – I’m still trying to figure out the inventory of who lives there, and how they matter to each other within that environment that the ecosystem services.”

Initially, she worked with Dr. Martel’s lab doing diversity and abundance studies of what’s in the river.

“That meant a lot of groping around in the bottom of the river, learning how to identify the mussels and count them,” she said. “But that knowledge was invaluable for me, so that I could move forward knowing precisely what I was seeing inside the cave themselves.”

The cave had initially been surveyed by Dr. Dave Sawatsky, a hyperbaric physician in the military stationed at CFB Petawawa. It took him 15 years to map just over 10.5 km of submerged passageways.

“Dave’s interest was purely in making that map,” she said. “For him, the biology just wasn’t of interest. I can’t even begin to tell you how difficult it would have been, because of the size (of the caves), the lack of visibility, and the high flow through the cave system.”

She described what she found when she began working under the direction of the scientists.

“So, there’s 10.5 km of quarter inch rope, lined through the cave system, and that’s because sometimes we need it to pull (ourselves) through the system, because the flow is so strong, and anything smaller would just get ripped out seasonally.”

The cave area is underneath Fitzpatrick Island, mainland in Quebec and Ontario, and Allumette Island. “This is technically two separate cave systems, but one huge network,” she said. “The landscape above it is, for the most part, still pretty natural and undeveloped, which is great because it means that we can protect it, because everything that happens on the surface of the earth will soak into the ground and end up being returned to you or to the fish to drink.”

There is a considerable body of historical information about early European contact with the Indigenous population. The explorer, Samuel d’Champlain, wrote of meeting a chief on Morrison Island, located between Cotnam’s Island just east of Pembroke and Allumette Island.

“We also know about the area from William Logan, who in 1845, wrote in his field notes about seeing places where the water was disappearing into the ground, like little vortexes and boils coming out of the river,” she said. “And so, we know that he also would have been taken there by the local Indigenous people. So, what William Logan would have seen are things like these sinkholes, the resurgence is where water comes out of the ground and siphons where things are getting sucked into the cave system, like an underground river below the river.”

There is one cave open to which there is a road on the mainland so that it’s accessible to vehicles.

“For every other cave dive that I need to do in this area, I either have to hike through the bush, paddle, or just last summer, I got myself a small little inflatable with an electric motor. I call it a kayak, but it’s really a paddle board and it’s piled up with stuff.”

While the opening of the cave accessible by car is relatively convenient, the cave goes under a little land bridge, under a sinkhole – one of many – and then off into the river.

“Just in case you ever thought you ever wanted to dive in the cave, this is to tell you, don’t,” she said. “As I mentioned, it’s very, very high flow, very, very low visibility, one to two feet in general, and very difficult conditions. We have 10.5 km of line inside the cave to aid with navigation, but some of the passageways are as wide as 50 feet. If you’ve got one to two feet of visibility, and the cave is 50 feet wide, it’s very easy to get lost.”

She has identified five different species inside the cave. In a square meter, there might be 100 mussels covering the floor, and then covered by sponges and other invertebrates.

“I’ve done over 8,000 dives in my life,” she said. “I’ve dived all the world, working with scientists and doing my own exploration and television work, and I’ve never seen anything like this. It’s a really exciting opportunity to be able to document, but it’s also really exciting to envision, as Andre mentioned, one to two liters of water per hour per mussel, and there’s millions, tens of millions, maybe hundreds of millions of mussels, in the cave and the river. That’s an ecosystem service that cannot be duplicated with machinery and mechanics. It’s doing such an important service for the river if we support it and protect the fish population too.”

Video Recordings Supported With Sketches

Multitasking is the order of the day for a cave diver collaborating with a team of scientists. Not only must she continually monitor and correct, when necessary, the functioning of the equipment that keeps her alive; she must also operate the camera to record what she encounters. But the camera is not her only recording tool; she also draws sketches.

“All of these drawings that you see in my presentation, these are my sketches that I do as I find a new animal, and I want to learn about that animal’s place in the ecosystem, or how to identify it for the future. When I draw, it helps me to remember,” she said.

For explorer-scientists, a discovery creates a conflict about how hands-on their investigations should be.

“What happens if the mussel is not in its proper feeding position? If you actually pick up a mussel to identify it, we want to put it back in the ground exactly the same way, because if you don’t, it takes 48 minutes for the mussel to right itself. And, that’s just from being laid down on the silt. These kinds of things are important to know, so that we can make good suggestions about whether it’s okay to touch a mussel or not, or collect it, or whether we should just be doing visual observations.”

Since the area being explored was once an ancient seabed, fossils are among the wonders seen inside the caves.

“We see coral remains, we see nautiloid shells, sometimes on the ceiling of the cave, and sometimes eroded out of the ceiling, when they’ll actually eventually drop to the floor. When they do, they become a new substrate for things to grow on top of,” she said.

The explorer not only sees the great variety of life in the cave; she also hears and feels it.

“The freshwater drum makes a very distinctive sound when they’re at their spawning season,” she said. “And the sturgeon, I get to feel them, because every once in a while, I get hit by one. When you startle them, and they take off, they sometimes give you a couple of slaps along the way. Dave, the fellow that did the original exploration of the cave, actually got one all entangled in his regulator hoses once, and it was flapping and beating him half to death before it removed the regulator from his mouth.”

Luckily for the Hickorynut mussels, there are no Zebra mussels in this stretch of the water so far. The Zebra mussel, an invasive species from Europe, is a serious threat because it attaches to native mussels and can kill them by interfering with breathing, feeding, excretion and movement.

“Is it because it’s remote?” she asks. “Maybe, but more likely it’s the water chemistry. There is not enough calcium for the building of their shells. The native mussels that are much thicker take longer to grow and could be more patient about their growth. The chemistry of the water supports the native mussels, but maybe can’t support those invaders for now. It doesn’t mean it’s going to stay that way. We should all be really careful about our boats and equipment.”

Ms. Heinerth decontaminates her diving equipment to ensure that no organic matter hitchhikes on it from one area to another.

Ongoing explorations confirm that the cave contains far more than mussels and fish.

“It’s a very vibrant ecosystem,” she explains. “It’s probably going to take me the rest of my life to continue working on it, but it’s something I feel is really important to protect such an incredibly isolated Eden. Even something as beautiful as this and as quiet as this region still can’t escape human kinds of bullets.”

To her dismay, she finds large big chunks of trash, ranging from tires to an entire stairway, in the caves. Also, there are many very large logs that were sucked into the caves during the decades when log drives on the river were the primary way of transporting timber to its ultimate users.

Adding even more urgency to the studies of the life in the section of the Ottawa River between the Rolphton and Chenaux hydro dams is that this part of the watershed is shared with the Canadian Nuclear Laboratories at Chalk River, the site of the world’s first nuclear meltdown in 1952.

“I’m sure many of you remember that it was scary – or maybe it wasn’t,” she said. “I would be interested in hearing your personal reflections. But at the time the operators knew that ‘oh boy, this isn’t good.’ So, this summer I’m going to carve out some time to make sure I do a survey upstream so that we can see if there’s other things living upstream and if there is a difference from what’s here.

“Observationally I can’t really say much, because I spent just a couple of days of surveying. Except – I only found two species (of mussels) in that part of the river. I thought a lot of the dead shells were extremely crumbly compared to what I was used to in other areas, and my brother did make me a little mini-Geiger counter which showed that they (the shells) did have some background signature of radioactivity.

“So, yeah – I’ve been digging around in the silt and who knows when I’ll grow a third eye. But it’s important to know these things, right? If these mussels are such great filter feeders, are they containing some of that nuclear waste, PFAS chemicals, what are they containing? That’s of great interest to me because it really exemplifies their importance as an ecosystem service in protecting our waterways.”

She left the audience with some take-home points.

“This is the longest underwater cave in Canada,” she said. “It’s a unique habitat that’s unlike anything we’ve seen or documented on the planet so far. So, in my opinion, we should seek some sort of special recognition or conservation designation for this segment of the Ottawa River. But that really is also up to you as the local citizens. And we’d like to know how we can better support you with information on what we’re doing.”

She invited the audience to contact her if they have any location they would like to have surveyed.

“Like, if there’s a sinkhole on your property and you’re wondering is this attached to a cave system and you just want someone to jump in and let you know what’s going on, I’d be happy to do that too.”

She noted that educational resources, including some newly-created ones, are available from the Royal Canadian Geographical Society, and these materials are being produced for free for schools across the country. Currently over 30,000 teachers are using these resources.