La Grande Rivière, 893 km long, rises in the rugged forest highlands of central Québec and drains west into James Bay. Its 97 600 km2 drainage basin is the third-largest in Québec. The river district has long been populated by Cree, whose hunting territories stretch along to its banks and tributaries. In 1803 the establishment of a fur-trade post at the river mouth marked the origins of the modern native settlement of Fort George. For many years the river too was called the Fort George.

During the 1970s it was transformed by the James Bay Project, a scheme to divert major rivers flowing into eastern James Bay for hydroelectric development. Phase one of the project involved erecting huge dams on the La Grande and flooding low-lying areas to create reservoirs. After a prolonged legal dispute, an agreement was signed with the native people who feared the destruction of their wildlife resources, and construction on the river was completed.