Ottawa, Or Grand, a river of Canada, rising in the X. W. portion of the province of Quebec, in about lat. 47° N. and lon. 7G° 30' W. It flows first N. W., then W., in a tortuous course through extensive lakes, for about 300 m., to Lake Temiscamingue (about lat. 47° 30', lon. 79° 30'), whence it pursues a S. E. course of about 400 m., separating Quebec from Ontario, and empties into the St. Lawrence at the upper end of the island of Montreal. The Ottawa has an irregular width, being lost in portions of its course in lakes through which it flows, while in others the waters contract to 40 or 50 yards, and are precipitated over rocks, sometimes forming beautiful cascades. Lake Temiscamingue has a length of 67 m. and a width varying from a few hundred yards to perhaps 10 m. The lower 24 m. of the river has a width of from 1 to 6 m., and is called the lake of the Two Mountains. About 75 and 95 in. respectively above the city of Ottawa are Calnmet and Allumette islands, belonging to Quebec; and 6 m. above Ottawa commence the rapids which terminate in the celebrated Chaudière falls, where the waters plunge 40 ft. and partly disappear by an underground passage, the outlet of which is unknown.

The river is navigable below Ottawa and for more than 160 m. above it, the rapids and falls being avoided by means of canals. The Rideau canal, from Ottawa to Kingston, opens a navigable connection with Lake Ontario. The chief tributaries of the Ottawa from the west are the Montreal, which enters Lake Temiscamingue, the Mattawan, the sources of which approach within a few miles of Lake Nipissing, the Petawawa, the Bonne Chere, the Madawaska, the Mississippi, the Rideau, which enters at the city of Ottawa, and the South Petite Nation. From the east it receives the Keepawa, a little below the mouth of the Montreal, the Du Moine, the Gatineau, nearly opposite Ottawa, the Du Lièvre, the North Petite Nation,' the Rouge, and North river, or Riviere du Nord. The Gatineau has a length of 400 m., and most of the other tributaries named vary from 100 to 250 m. The Ottawa and its tributaries drain an area estimated at 80,000 sq. m. The valley of the Ottawa abounds in timber, particularly red and white pine, and forms one of the. most productive lumber regions in the world.