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The Grand River flows 290 km south from just below Georgian Bay in south-central Ontario to the northeast end of Lake Erie. Its 6965 sq. km watershed drains the historic heartland of Ontario, discharging more than two cubic kilometres of water per year. The Nith, Conestogo, Speed and Eramosa rivers are the main tributaries of the Grand, whose waters eventually flow over the Niagara Falls on their journey down the Great Lakes-St. Lawrence waterway to the Atlantic Ocean.