The Moose River is 547 km long from the head of its tributary, the Mattagami River. It is formed by the confluence of the Mattagami and the Missinaibi rivers, and flows northeast 104 km to discharge into the bottom of James Bay in northern Ontario. With its tributaries (also the Abitibi, Groundhog, Kapuskasing and Kwataboahegan rivers), it drains most of the northeastern part of the province. Once well travelled by fur traders, the river basin today is the site of mining, pulp and paper, and hydroelectric developments. Moose Factory, Ontario's oldest trading post (est 1672-73), is located on an island near the river's mouth, opposite the mainland town of Moosonee, Ontario's only saltwater port. The Ontario Northland Railway links these settlements to the south.