La Grosse Île, or Île de Quarantaine, 2.9 km long by 1 km wide, is located 46 km downstream from Québec City in the ST LAWRENCE RIVER estuary. The island is a wooded Appalachian ridge sculpted by coves and capes. In 1646 the Île de Grâce was ceded to Governor Charles Huault de MONTMAGNY.
Rivière Saint-Maurice, 563 km long, rises upstream from Réservoir Gouin, 200 km west of Lac Saint-Jean, Québec. It drains a basin of 43 300 km2. After its confluence with Rivière Manouane, it feeds Réservoir Blanc and then takes in the Vermillon, Trenche, Croche, Mattawin and Mékinac rivers.
A continental divide is a ridge or natural boundary of elevated terrain that separates the drainage basins of a continent. Each drainage basin contributes its water to river systems, which in turn flow into distinct larger bodies of water, such as oceans. The main continental divide in Canada follows the ridge of the Rocky Mountains.