The Rivière Eastmain, 756 km long, rises in the central part of Québec on the side of a low drainage divide from which streams flow west to James Bay. The river encounters a sharp break of slope coming off the Canadian Shield peneplain as it meets the narrow coastal plain of James Bay, and in its final 65 km descends 125 m in a series of rapids and falls. The river's drainage basin is situated in an area of heavy snowfall, resulting in an impressive mean discharge. Most of its flow has been diverted into the La Grande Rivière to produce hydroelectricity.
See also James Bay Project.