It was 8 in the morning, and a fine September day was breaking over the Ottawa Valley. I was headed that day for the small village of Quyon, Quebec, with my scuba-diving and sampling equipment. At the village, a small ferryboat brought me to Mohr’s Landing, on the Ontario side of the Ottawa River, in less than 10 minutes.

Anyone who takes the Quyon ferry can only marvel at the majesty and rich history of the Ottawa River. With a width of almost one kilometre at this location, its lush, wooded banks and vast grass beds of aquatic plants are an ideal habitat for waterfowl. If you pay no attention to the hydroelectric station just a few kilometres upstream, the area displays an apparently healthy shoreline, in a peaceful setting resembling genuine wilderness.

Three people stand together at the boat launch.
Andy, Nancy and André, before leaving to dive off MacLaren’s Landing, on the Ottawa River. Image: Jacqueline Madill © Canadian Museum of Nature

I know from the many dives I have made that the subaquatic fauna in this river is fascinating. And the best way to study it is to go scuba diving! My research focuses in particular on freshwater mussels, which some people call freshwater clams. While crossing the river, I thought to myself that just under the hull of the ferryboat, there were millions of these big mussels spread out over just a few kilometres of river.

These mussels serve a very useful purpose, for both the aquatic ecosystem and the humans living along the banks. Thanks to their gills, mussels filter thousands of litres of water each year. They live on plankton in the water, but also on detritus and even human and agricultural fecal coliforms. During their lifetime, mussels nobly serve the cause of humanity by purifying the water of our rivers and lakes.

View of a mussel that focuses on the opening of its shell.
A close-up of a black sandshell mussel (Ligumia recta) filtering the water of the Ottawa River at a depth of 3 m. Note the longer papillae around the inhalant siphonal aperture, where water and plankton enters into the animal, compared with exhalent aperture (upper right). Image: André Martel © Canadian Museum of Nature

By the time I was finished musing, the ferryboat was docking on the opposite shore. After a five-minute car ride, I was on the boat launch at MacLaren’s Landing, the small community where I was to join up with my team. It was now 9 a.m.

Nancy, Andy and Jacquie arrived in turn at the meeting point. Nancy, an experienced diver interested in conservation of the Ottawa River, was my diving partner for this outing. Andy, her partner and also an able diver, was in charge of steering his 4.3-metre inflatable boat—a craft ideally suited for diving. As for Jacquie, she would serve as our research assistant.

A pick-up truck with a boat on a trailer, boxes of equipment and two men.
Andy (right) gets the inflatable dive boat ready while André (left) brings diving gear. In the foreground are one-metre quadrants that are used when sampling mussels. Image: Jacqueline Madill © Canadian Museum of Nature

We left shore around 10:30 a.m. and headed for the middle of the river, west of Mohr Island, virtually on the Quebec–Ontario boundary line. We were in the middle of a large sandy zone, with a water depth of three to five metres. Our goal that day was to make two dives of about 30 to 40 minutes each to collect data on the diversity and number of mussels living in the area.

A mussel out of the water on a piece of wood.
A live male black sandshell mussel (Ligumia recta), measuring about 12 cm in length. Image: Jacqueline Madill © Canadian Museum of Nature

At 11 a.m., Nancy and I slipped into the water at the first sampling site. The water temperature was 16°C. At a speed of about 10 cm per second, the current was moderately fast—a flow rate that many mussel species prefer to still water.

Guided by the anchor rope, Nancy and I reached the sandy river bottom at a depth of 3.5 m. The visibility of almost 4 m allowed us to make out the blackish hull of the boat.

A riverbed showing partially buried mussels.
A plain pocketbook mussel (Lampsilis cardium; bottom) and an eastern elliptio (Elliptio complanata; upper right) filtering water, side by side in the Ottawa River near MacLaren’s Landing. Image: André Martel © Canadian Museum of Nature

Nancy and I carried a quadrat along with us, which is in fact a big, rigid, plastic frame measuring one square metre. We set the frame down on the river bottom and collected all the live mussels inside it, including those slightly covered in sand and barely visible.

We put the mussels in a large sampling bag specially designed for diving. A quick glance at the bag allowed me to estimate that we would easily exceed 100 individuals per square metre at this location. Once this first bag was sealed, we swam upstream with our equipment for about one minute and repeated the operation.

Clips of two divers at the surface, sometimes holding sampling quadrants and bags of mussels. The divers comment on the lack of underwater visibility and the large amount of mussels they observed.

Once the collecting was done, we swam to the surface and climbed back into the boat. This brief excursion out of the water would have little impact on the live mussels. We took the boat a few hundred metres northwest, where we made a second dive and repeated the procedure. Once this sampling was finished, we returned to shore for a well-deserved lunch, after sampling a total surface area of four square meters of river bottom. By this time, it was 12:45 p.m.

Team members measure, sort and identify the mussels collected in one of the samples. They comment on the size of the mussels and their relative abundance.

On shore, we identified, counted and measured the mussels one by one. There were at least 300 of them. We were lucky that day: our first quadrat included a rare hickorynut mussel, an endangered species in Canada. It can be found in only six rivers in Canada, and the Ottawa River is one of those.

Two photos, each showing a mussel.
On left: A live specimen of a hickorynut mussel (Obovaria olivaria), collected in the Ottawa River, west of Mohr Island, in 3 m of water. This species is endangered in Canada. This specimen is estimated to be 15 to 20 years old. On right: A female plain pocketbook mussel (Lampsilis cardium), photographed underwater off MacLaren’s Landing, in the Ottawa River. Images: André Martel © Canadian Museum of Nature

In addition to the hickorynut, there were four other species in our bag: the abundant eastern elliptio, eastern lampmussel, plain pocketbook and black sandshell. The numbers of our four samplings spoke for themselves: 164, 130, 146 and 136 mussels respectively. These were impressive numbers, and very high compared to other rivers in the region. What’s more, the Ottawa River harbours 16 of the 55 species of freshwater mussels found in Canada, i.e., almost 30% of freshwater mussel varieties.

An array of two kinds of mussels on a wooden board.
Eight eastern elliptios (Elliptio complanata) and six plain pocketbook mussels (Lampsilis cardium) on a wooden board before being measured and released back into the Ottawa River at the sampling location. Image: Jacqueline Madill © Canadian Museum of Nature

Once the analyses were completed, Andy and Jacquie went back on the water to release the live mussels at the spots where they were picked up. It was now 4:30 p.m. and we packed up our equipment.

By repeating this type of outing, we will eventually be able to describe in a detailed fashion the distribution and abundance of various freshwater mussel species in this river.

Several mussels on a towel.
In the upper row are two live, adult eastern lampmussels (Lampsilis radiata). The other four are live plain pocketbook mussels (Lampsilis cardium). Note the morphological differences between the two male pocketbooks on the left and the females on the right. Image: Jacqueline Madill © Canadian Museum of Nature

But that time, though, it was 5 p.m.; time to return home and warm up over a comforting supper! Back on the ferry, I reflected on this little known fauna living on the bottom of this great river, the millions of mussels that live partially buried in the beautiful sand like faithful sentries, filtering the river’s water all day long.

A wonderful day of work had just come to an end.

Translated from French.