The Petawawa River is a river in the Saint Lawrence River drainage basin in Nipissing District and Renfrew County in eastern and northeastern Ontario, Canada. The river flows from Algonquin Provincial Park to the Ottawa River at the town of Petawawa, and is only one of two major tributaries of the Ottawa River to flow completely free (the other being the Dumoine River). The river's name comes from the Algonquian for "where one hears a noise like this", which refers to its many rapids.