OTTAWA, the largest tributary of the river St. Lawrence; ranking ninth in length among the rivers of Canada, being 685 m. long. It flows first westward to Lake Timiscaming; thence south-east and east. The principal tributaries on the left bank are the Rouge (115 m.), North Nation (6o), Lievre (205), Gatineau Coulonge (135), Dumoine (8o); and on the right bank, the South Nation (90), Mississippi (ios), Madawaska (13o) and Petawawa (95). Canals at Ste. Anne, Carillon and Grenville permit the passage of vessels drawing 9 ft., from Montreal up to the city of Ottawa. At Ottawa the river is connected with Lake Ontario by the Rideau Canal.
The Ottawa was first explored by Samuel de Champlain in 1613. Champlain describes many of its tributaries, the Chaudiere and Rideau Falls, the Long Sault, Chats and other rapids, as well as the character of the river and its banks, with minuteness and reasonable accuracy. The Long Sault Rapids on the Ottawa,
about midway between Montreal and the capital, were the scene of one of the noblest exploits in Canadian history, when in 1661 the young Sieur des Ormeaux with sixteen comrades and a hand ful of Indian allies deliberately gave their lives to save New France from an invasion of the Iroquois. They intercepted the war party at the Long Sault, and for nearly a week held them at bay. When finally the last Frenchman fell under a shower of arrows, the Iroquois were thoroughly disheartened and returned crestfallen to their own country. For a hundred and fifty years thereafter the Ottawa was the great highway from Montreal to the west for explorers and fur-traders. Throughout the 19th century the Ottawa was the thoroughfare of lumbermen, whose immense rafts went from its upper waters to Montreal and Quebec.