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".

The Ottawa-Bonnechere Graben is a geological structure that coincides with a 55 km (34 mi) wide topographic depression extending from near Montréal through Ottawa. It is part of the Saint Lawrence rift system that also includes the seismically active Saguenay graben. This rift valley was formed when the Earth's crust moved downward about a kilometre between two major fault zones known as the Mattawa and Petawawa faults.