Deep River is a town in Renfrew County, Ontario, Canada. Located along the Ottawa River, it lies about north-west of Ottawa on the Trans-Canada Highway. Deep River is opposite the Laurentian Mountains and the Province of Quebec. The name "Deep River" purportedly derives from the fact that the Ottawa River reaches its greatest depth of just outside the township. However, the Ottawa River today reaches a depth of in Moose Bay which is located on the Holden Lake reservoir from the Des Joachim dam, west of Deux-Rivières.