The Ottawa River (, Algonquin: Kichi-Sìbì/Kitchissippi) is a river in the Canadian provinces of Ontario and Quebec. It is named after the Algonquin word 'to trade', as it was the major trade route of Eastern Canada at the time. For most of its length, it defines the border between these two provinces. It is a major tributary of the St. Lawrence River and the longest river in Quebec. Geography 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. 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 long; it drains an area of , 65 per cent in Quebec and the rest in Ontario, with a mean discharge of . It has a maximum depth of at the Carillon Reservoir and is wide at its widest part. The average annual mean waterflow measured at Carillon dam, near the Lake of Two Mountains, is , with average annual extremes of . Record historic levels since 1964 are a low of in 2010 and a high of in 2017. The river flows through large areas of deciduous and coniferous forest formed over thousands of years as trees recolonized the Ottawa Valley after the ice age. Generally, the coniferous forests and blueberry bogs occur on old sand plains left by retreating glaciers, or in wetter areas with clay substrate. The deciduous forests, dominated by birch, maple, beech, oak and ash occur in more mesic areas with better soil, generally around the boundary with the La Varendrye Park. These primeval forests were occasionally affected by natural fire, mostly started by lightning, which led to increased reproduction by pine and oak, as well as fire barrens and their associated species. The vast areas of pine were exploited by early loggers. Later generations of logging removed hemlock for use in tanning leather, leaving a permanent deficit of hemlock in most forests. Associated with the logging and early settlement were vast wild fires which not only removed the forests, but led to soil erosion. Consequently, nearly all the forests show varying degrees of human