The Missinaibi River is a river in northern Ontario, Canada, which flows northeast from Missinaibi Lake, north of Chapleau, and empties into the Moose River, which drains into James Bay. This river is 755 kilometres (469 mi) in length. It is one of the longest free-flowing and undeveloped rivers in Ontario.

The Moose River is a river in the Hudson Plains ecozone of northern Ontario, Canada. The river flows 100 km northeast from the confluence of the Mattagami and Missinaibi Rivers into James Bay. Its drainage basin is 108,500 square kilometres (41,900 sq mi) and it has a mean discharge rate of 1,370 cubic metres (48,000 cu ft). Its full length is 547 kilometres (340 mi) if counted from the head of the Mattagami River.