Attawapiskat River, river in northern Ontario, Canada, that issues from Attawapiskat Lake (elevation 815 feet [248 metres]) and flows eastward into James Bay, opposite Akimiski Island. For most of its 465-miles (748-km) course, the river is sluggish and navigable only for canoes. Its lower reaches are dotted with islands and lead through swamp country. The surrounding region is uninhabited except for the trading posts of Attawapiskat, near the river’s mouth, and Lansdowne House on Attawapiskat Lake.