|Big Rideau Lake|
|Location||Lanark County, United Counties of Leeds and Grenville, Ontario|
|Part of||Saint Lawrence River drainage basin|
|Primary inflows||Black Creek, Rideau River|
|Primary outflows||Rideau River|
|Catchment area||407 square kilometres (157 sq mi)|
|Max. length||32 kilometres (20 mi)|
|Max. width||6 kilometres (3.7 mi)|
|Max. depth||360 feet (110 m)|
|Surface elevation||123.1 metres (403 ft 10 in)|
|Settlements||Portland, Rideau Ferry|
Big Rideau Lake is a lake in the municipalities of Tay Valley and Drummond/North Elmsley, Lanark County and Rideau Lakes, United Counties of Leeds and Grenville in Eastern Ontario, Canada. The lake is on the border between the two counties, 72 kilometres (45 mi) to the southwest of Ottawa. It is 32 kilometres (20 mi) long and is 6 kilometres (3.7 mi) wide, is much narrower at its northeastern end than at its southwestern end, and is part of the Saint Lawrence River drainage basin. It is the largest lake on the Rideau Canal, which was designated a UNESCO world heritage site in 2007.
The primary inflow, at the southwest, is the Rideau River/Rideau Canal from Upper Rideau Lake via The Narrows channel and the Narrows lock and control structures. A second primary inflow is Black Creek at the west. The primary outflow, at the north, is also the Rideau River/Rideau Canal which leads via a channel to Lower Rideau Lake. The Rideau River and Canal flow to the Ottawa River and then to the Saint Lawrence River.
The small community of Rideau Ferry is located at the junction between the Big Rideau and Lower Rideau Lake, at the northeastern end of the lake. The community of Portland is located along the southern shore of the lake.
The shoreline of the Big Rideau Lake is lined with hundreds of cottages and houses. A public recreation area and campground, Murphys Point Provincial Park, is located along a substantial stretch of the shoreline on the northern side of the lake.
The Big Rideau Lake Association (BRLA) is a non-profit organization that was formed in 1911, and operates summer programs from Cow Island, one of the many islands in Big Rideau. Its purpose is "to preserve and enhance the quality of life on Big Rideau Lake." The BRLA places private shoal markers throughout the lake, marking hazards underwater at some times in the navigational season. A group of markers indicate the extent of a shoal: go around, not between.
The International Big Rideau Lake Speed Skating Marathon is an annual event.
- Rideau River
- Black Creek
- "Subwatershed Reporting — Rideau Lakes". Rideau Valley Conservation Authority. 2014. Archived from the original on 2015-07-22. Retrieved 2015-07-20.
- "Rule Curves for the Rideau Lakes". Ken W Watson. Retrieved 2015-07-20.
- "Big Rideau Lake". Geographical Names Data Base. Natural Resources Canada. Retrieved 2015-07-20.
- "Rideau Canal". UNESCO. Retrieved 2012-08-27.
- Paulina Hrebecka, "Portland historical society honours founding father of Royal Canadian Navy," Smiths Falls Record News, August 26 2019
Other map sources: