Ottawa River

About the Ottawa River

Around 1.7 billion years ago in the Precambrian Era, the continental plates that make up present-day Africa, Antarctica, Asia, Australia, Europe and South America began to converge on North America. Successive masses of rock were thrust upon the North American plate, whose eastern edge at that time was near Sudbury. This converging climaxed 1.1 billion years ago when South America, West
Africa and Europe collided with North America. This formed the supercontinent Rodinia , composed of the oldest rocks in the watershed.

The collision of great continental plates and smaller continental fragments pushed their edges higher and higher, creating the mighty Grenville Mountains, taller than the Himalayas. The mountains eroded away over the next 200 million years, leaving only stumps. The rocks we see today were once buried as much as 20 to 30 kilometers below the mountain summits.  The immense size of the Grenville Mountains can be judged by the fact that their base, represented by Grenville age rocks, extends east to a point near the Quebec-New Brunswick border.

Around 800 million years ago the supercontinent Rodinia started breaking apart into separate smaller continents, separated by ever-widening oceans. Around 600 million years ago, lighter rocks within the Earth’s crust pushed upward and cracked the still-massive supercontinent.  One of the arms in the crack began as a massive split in the Gulf of St. Lawrence to the east, extending westward along the Ottawa up through Lake Timiskaming, and along the Mattawa River to Lake Nipissing. This is one of Earth’s greatest rift valleys. It contained breaks or “faults” extending 40 km deep into the Earth’s crust. Had the rift valley continued to grow, Pontiac County and Renfrew County would today be on opposite sides of an ocean.

As the split in the Ottawa and Bonnechere valleys widened and deepened during the Mesozoic Era, portions of the land in the region slumped downward, creating the Ottawa-Bonnechere Graben (a graben is an area of down-dropped land between two major faults), within which segments of Ordovician strata were preserved. The Ottawa River occupies the major fault at the northern edge
of the graben. The southern boundary of the graben is the Mount Saint Patrick fault, straddling the Bonnechere and Madawaska watersheds.

Why is the Ottawa River so important?

The Ottawa River Valley is home to at least 24 provincially or nationally imperilled species, including Least Bittern, Spotted Turtle, and American Ginseng. Its microclimate, sand, and limestone substrate sustain rich wetland and forest habitats that support a diversity of flora and fauna. While the region is one of the most threatened landscapes in Canada, it hosts the most biologically diverse ecosystems in Québec. (Source: The Nature Conservancy)

The Ottawa River is also home to a unique and diverse fauna of freshwater mussels. This unique freshwater mussel fauna includes a minimum of 14 different species (27 % of the Canadian freshwater mussel fauna), each one linked to specific fish hosts which ensure the upstream and downstream dispersal of the mussel’s specialized glochidia larvae. In many areas of the Ottawa River, the density of freshwater mussels on the bottom commonly exceeds 100 individuals per square metre. This is a very high value compared to other rivers in Eastern Canada. (Source: André Martel – Canadian Museum of Nature)

What kind of wildlife and plants are found here?

You’ll find lots of wildlife along the river – not just Canada Geese! During the spring and fall you can see and hear songbirds like Warblers and Vireos moving through the region, and huge groups of Ring-billed gulls, Herring and Great Black-backed gulls, and tens of thousands of waterbird species. August is ideal for watching Great Egrets on the move southward, and you may even spot some shorebirds moving through and feeding on exposed mud flats (when the river is low).

And you’ll see other critters, too!  to be continued
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