Lac Deschênes (French pronunciation: [lak deʃɛn]) is a 44 kilometres (27 miles) long lake on the Ottawa River that runs from the Chats Falls Dam near Fitzroy Harbour in the west to the Deschênes Rapids at Britannia in the east.

On the Quebec side of the lake is the Club de Voile Grande-Rivière located at the Aylmer Marina.

Access between Ontario and Quebec across Lac Deschênes is provided by a ferry service between West Carleton and Quyon.

[12][13] Canadian Hydrographic Service Chart 1550 - Britannia Bay to Chats Falls covers the whole of Lac Deschênes.

Although much of Lac Deschênes is relatively shallow, generally less than 9.0 m, there is a deep trough between Twelve Mile Island and Aylmer Island that reaches depths of 49 m.[18] Numerous species of sport fish can be found in Lac Deschênes including black crappie, pickerel (walleye), muskie, and pike.

Moderate numbers of shorebirds concentrate in the muddier parts of the shoreline such as at Shirleys Bay and Andrew Hayden Park.

[21] In August 2023, Jean-Pierre Caron, a resident of Aylmer, proposed the creation of a pedestrian bridge connecting Deschênes to Britannia.

Hull-Aylmer MP Greg Fergus stated the federal government is not close to funding the project, while residents in Ottawa have expressed environmental and traffic concerns.

[22] The National Capital Commission (NCC) stated they would consider the bridge plan in their 2024 evaluation of the circulation and interprovincial travel needs of the region.