File:Water Taxi Across Ottawa River, Ottawa, Ontario (30035255306).jpg

The Ottawa River (French: Rivière des Outaouais, Algonquin: Kitchissippi) is a river in the Canadian provinces of Ontario and Quebec. For most of its length, it defines the border between these two provinces. It is a major tributary of the St. Lawrence River.

The river rises at Lac des Outaouais, north of the Laurentian Mountains of central Quebec, and flows west to Lake Timiskaming. From there its route has been used to define the interprovincial border with Ontario. The river reaches great depths of nearly 460 feet in some places.

From Lake Timiskaming, the river flows southeast to Ottawa and Gatineau, where it tumbles over Chaudière Falls and further takes in the Rideau and Gatineau rivers.

The Ottawa River drains into the Lake of Two Mountains and the St. Lawrence River at Montreal. The river is 1,271 kilometres (790 mi) long; it drains an area of 146,300 square kilometres (56,500 sq mi), 65 percent in Quebec and the rest in Ontario, with a mean discharge of 1,950 cubic metres per second (69,000 cu ft/s).

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