The river starts at Ralph Bice Lake in northern Algonquin Provincial Park in the geographic township of Butt in the Unorganized South Part of Nipissing District. It flows south to Daisy Lake then east to Big Trout Lake. The river heads north out the lake over Big Trout Lake Dam, takes in the left tributary Tim River, flows over the Portal Rapids, Cedar Rapids, Snowshoe Rapids, Catfish Rapids, and Stacks Rapids to reach Cedar Lake, the location of the community of Brent, where it takes in the left tributary Nipissing River. The river exits the lake over a dam, heads through the Devil's Chute, reaches Radiant Lake, where it takes in the left tributary North River and right tributary Little Madawaska River, and passes through the Squirrel Rapids, Big Sawyer Rapids, Battery Rapids Cascade Rapids and White Horse Rapids, and takes in the right tributary Crow River. The river then continues through a series of rapids including the Devil's Cellar Rapids, passes the Algonquin Radio Observatory, and reaches Lake Travers. The Petawawa River enters a canyon and passes through numerous rapids including the Big Thompson Rapids, Little Thompson Rapids, Grillade Rapids, Crooked Chute, Rollway Rapids, The Natch, Schooner Rapids, Five Mile Rapids to arrive at Whitson Lake adjacent to the Petawawa Hills. It leaves Algonquin Provincial Park and enters the municipality of Laurentian Hills in Renfrew County, continues southeast past CFB Petawawa, passes through the Crooked Rapids, Race Horse Rapids, White Horse Rapids and Halfmile Rapids, and reaches Lac du Bois Dur, where it takes in the right tributary Barron River. The river enters the town of Petawawa, heads under Ontario Highway 17, through the Big Eddy Rapids, under the Canadian Pacific Railwaymain line, and empties into Black Bay on the Ottawa River. The river is in length and drains an area of, with a mean discharge of per second.
Economy
From the late 19th century until the 1960s, the river was used for log driving of the timber from the forested areas surrounding the river. The river is visited by canoeing and kayaking enthusiasts - both for its white water rapids and its views. In 2009, based on subsidized power-generation rates in the Ontario Green Energy Act's Feed-in-Tariff program, there were plans to build a 5.3 MW hydro-electric generating station at Big Eddy Rapids, about upstream from the river's mouth. The project involved building a concrete and boulder weir that would direct a portion of the water to a new long intake channel and powerhouse, as well as a fish ladder. It was scheduled to be operational by 2015, but the project raised opposition from the local communities, paddlers, and environmental groups. Both Big Eddy Rapids and Half Mile Rapids would have been affected. The project was among nineteen FIT hydro projects on ten rivers that were cancelled in 2015 after their FIT contracts were terminated following the opposition by groups like the Ontario Rivers Alliance.
