Sinkhole on Gervais property, Ottawa River Valley (Photo by Daniel Brunton).

Sinkhole on Gervais property, Ottawa River Valley (Photo by Daniel Brunton).

Gervais Caves, Ottawa River Valley

Channel spring, Gervais property, Ottawa, ON (Photo by Daniel F. Brunton).

Channel spring, Gervais property, Ottawa, ON (Photo by Daniel F. Brunton).

Did you know that the Ottawa River Valley is home to the longest underwater cave system in Canada? Beneath the surface of the Ottawa River lies a subterranean wonderland seldom seen by the human eye — the Ottawa River Caves. The labyrinth measures over 10 kilometres in length and sprawls under several islands throughout the Ottawa River, including a four-kilometre section on the Ontario side of the river known as the Gervais Caves.

A conservation legacy

The Nature Conservancy of Canada (NCC) recently purchase a 75-acre (30-hectare) shoreline parcel that contains most of the entrances to the Ontario portion of this remarkable series of caves. The Gervais Caves property is a beautiful undeveloped shoreline site, featuring mature forests, riverine habitat, unique plant and animal species and a network of freshwater caves. This is the highest priority conservation property in the Ottawa River Valley, representing nationally significant earth and life science features. This property supports nationally and provincially designated species at risk and regionally significant vegetation and flora.

This area has been identified as a key area of biodiversity significance in both the Great Lakes and St. Lawrence Lowlands Conservation Blueprints — scientific plans based on biodiversity values, levels of threat and opportunities for conservation action.

Conservation values

The most important features of the property are the karst landscape and sinkholes associated with the Gervais property. Karst landforms are an important variant of landforms created by flowing water. Water is routed underground via solutional cave systems instead of flowing at the surface in normal river channels.

At least 13 of these sinkholes are connected to the Ottawa River through this extensive network of underwater caverns. Fish such as sturgeon, walleye and smallmouth bass can be found hiding in the nooks of the caves.

Ecological significance

“We spent a total of 752 hours underwater surveying the caves. There is no question the Ottawa Valley caves are the longest underwater caves in Canada (so far) but they are also significant Canadian caves in their own right,” said Dr. David Sawatzky, a retired Canadian Armed Forces lieutenant-colonel, doctor, diver and expert on cave diving who spent over 15 years mapping the Ottawa River caves.

Above ground, the Gervais property is just as impressive. This site is full of life — home to over 135 native vascular plant species and a number of at-risk plant species, including the endangered butternut tree, the provincially-rare Hooker’s orchid, regionally-rare moonseed and Hitchcock’s sedge. The mature forest features exceptionally large examples of Eastern white cedar, including two trees over 90 centimetres in diameter that are many centuries old.

The Ottawa River supports a rich diversity of freshwater mussels and at least 13 species of mussels have been recorded in this area. Freshwater mussels filter bacteria, microscopic algae and organic material contained in the water, which improves water quality and contributes to the aquatic ecosystem. The endangered and rare hickorynut freshwater mussel can be found in the Ottawa River. In order to filter food and consume nutrients, mussel larvae must attach to a fish, called a host. Hickorynuts attach to lake sturgeon to consume their nutrients from the fish’s body until they transform into juvenile mussels and fall off.

An important conservation opportunity

“I must say, having explored the Ottawa Valley landscape for some 45 years both in a professional and private capacity, I’ve never seen a place like this and I think it is an extraordinary and important conservation opportunity,” says Daniel Brunton, co-founder of the Ottawa Riverkeeper, who conducted site assessments of the Gervais property as an independent ecological consultant.

Click HERE to support work for the Gervais Caves.

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