The Mattawa River is a river in central Ontario, Canada. It flows east from Trout Lake east of North Bay and enters the Ottawa River at the town of Mattawa. Counting from the head of Trout Lake, it is 76 kilometres (47Â mi) long. The river's name comes from the Algonquin word for "meeting of waterways".
Two provincial parks are located along it: the Mattawa River Provincial Park stretches along both sides of the river's banks for almost its full length; and Samuel de Champlain Provincial Park, located about 10 kilometres (6.2Â mi) from the river's end.