What is the Ottawa River?

The Ottawa River (riviere des Outaouais) is the principal tributary of the St. Lawrence River, flowing about 1,271 kilometres from its source at Lake Capimitchigama in the Laurentian Mountains of Quebec southwest to its mouth at the Lake of Two Mountains, on the western tip of the Island of Montreal. The river drains a basin of about 146,000 square kilometres covering parts of Quebec and Ontario, the second-largest drainage basin in eastern Canada after the St. Lawrence.

The Ottawa River forms most of the boundary between Ontario and Quebec, from Lake Timiskaming in the north to the Lake of Two Mountains in the south. Major centres along the river include Mattawa, Pembroke, Renfrew, Arnprior, Ottawa-Gatineau (the National Capital Region, with Ottawa on the Ontario shore and Gatineau on the Quebec shore), Hawkesbury, and Lachute. The Chaudiere Falls in the heart of Ottawa-Gatineau dropped about 12 metres at the historic site of Indigenous portages and the Hudson's Bay Company trading post; the falls have been heavily reshaped by hydroelectric dams since the late 19th century.

The river was the principal route for the canoe-borne fur trade from the early 1600s. Algonquin and Anishinaabeg nations occupied the watershed and traded with the French. Etienne Brule and Samuel de Champlain explored the river between 1610 and 1613. The Ottawa River remained the main route to the Great Lakes and the upper continental interior until the railway era of the late 19th century. The Rideau Canal (built 1826 to 1832 by Lieutenant-Colonel John By to connect Ottawa to Kingston via the Rideau and Cataraqui Rivers) was a federal alternative defensive route that became one of Canada's most important heritage canals (UNESCO World Heritage Site since 2007).

The Ottawa River was central to the timber trade of the 1800s. Logs were rafted down the river from Pontiac County, Quebec and the Ottawa Valley, Ontario to Quebec City for shipment to Britain. The square-timber industry built fortunes in Ottawa, Bytown, and the Ottawa Valley. Modern uses include hydroelectric generation (Hydro-Quebec and Ontario Power Generation operate dams at Carillon, Chenaux, Chats Falls, Bryson, Otto Holden, and others), municipal water supply, and recreation. The Algonquin Anishinabeg Nation Tribal Council asserts unceded title to the river basin, with comprehensive land-claim negotiations ongoing since 1992.