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 (47 mi) long. The river's name comes from the Algonquin word for "meeting of waterways".

Trout Lake is a lake in the municipalities of East Ferris and North Bay, Nipissing District, Northeastern Ontario, Canada. It lies approximately 6 kilometres (4 mi) east of the much larger Lake Nipissing, with the city of North Bay in between them. Trout Lake is the source of the Mattawa River and a significant body of water on a well-known historic North American voyageur (fur-trading) route. It is about 11 kilometres (7 mi) long and 4 kilometres (2 mi) wide and exits eastward into the Mattawa River, which flows via the Ottawa River to the St. Lawrence River. Some of the most difficult portages are found on this part of the voyageur route between Trout Lake and the end of the Mattawa River, e.g., Portage de Mauvaise Musique, located at the Talon Chute.