|Location||Minnesota, USA / Ontario, Canada|
|Type||remnant of former glacial Lake Agassiz|
|Primary inflows||Namakan Lake
|Primary outflows||Rainy River|
|Basin countries||Canada, United States|
|Max. length||80 km (50 mi)|
|Max. width||48 km (30 mi)|
|Surface area||932 km2 (360 sq mi)|
|Max. depth||50 m (160 ft)
|Shore length1||1,500 km (930 mi)
2,520 km (1,570 mi) (w/ Islands)
highly irregular, rocky shoreline
|Surface elevation||338 m (1,109 ft)|
|Settlements||International Falls, MN
Fort Frances, Ontario
|1 Shore length is not a well-defined measure.|
Rainy Lake (French: lac à la Pluie; Ojibwe: gojijii-zaaga'igan) is a relatively large freshwater lake (345 square miles (890 km2)) straddling the border between the United States and Canada. The Rainy River issues from the west side of the lake and is harnessed to make hydroelectricity for US and Canadian locations. The sister cities of International Falls, Minnesota, and Fort Frances, Ontario, are situated on either side of the outflow of the river from the lake. Rainy Lake and Rainy River establish the boundary between the two countries. 
Voyageurs National Park is located on the southeastern corner of the lake, where it connects with Kabetogama and Namakan lakes. Rainy Lake is part of an extremely large system of lakes forming the Hudson Bay drainage basin that stretches from west of Lake Superior north to the Arctic Ocean. The Rainy Lake watershed includes the Boundary Waters Canoe Area Wilderness (BWCA), portions of the Superior National Forest on the US side of the border, and the Quetico Provincial Park on the Canadian side of the border.
Earliest documentation of the lake's name is "Tekamamiwen" (shown as "Lac de Tecamamiouen" on the Ochagach map (c. 1728), as "Lac Tacamamioüer" on the 1739 de l'Isle map, as "Lake Tecamaniouen" on the 1757 Mitchell Map and as "Lake Tekamamigovouen" on the Thomas Jefferys' 1762 Map of Canada). Pierre Gaultier de Varennes, sieur de La Vérendrye cites that the name was a corruption from the Cree "taki-kimiwen", meaning "It always is raining", referring to the Rainy River, though the language does not quite support that claim. He also cites that the lake was also known as "Ouichichick" (Ojibwe word Gojijiing or Cree Kocicīhk, both meaning "at the place of inlets"). Early documents lists the portion of Rainy Lake east of the Brule Narrows as "Cristinaux [Cree] Lake" or as "Little Lake."
Recreation on Rainy Lake
Voyageurs National Park
On Rainy Lake, Voyageurs National Park maintains an extensive network of over boat-in camping sites, hiking trails, and designated snowmobile trails for winter use.
The lake is popular for sport and recreational fishing for species such as Walleye, Northern pike, Muskellunge, Largemouth and Smallmouth bass, which are all considered excellent freshwater sportfish. Rainy Lake is home to the annual Canadian Bass Championship, which has occurred every summer since 1996. The lake is dotted with many small islands on both the Canadian and American sides; they are the sites of numerous fishing cabins, small fishing resorts, and vacation homes. Tourism is an important part of the local economy.
The level of Rainy Lake is controlled at the hydro-electric power houses of the international dam that spans the Rainy River between International Falls and Fort Frances, at two water-control dams located at Kettle Falls where the outflow from Namakan Lake enters Rainy Lake, and at the Sturgeon Falls Generating Station located on the Seine River. The companies that own and operate the powerhouses (Boise Inc. on the U.S. side and H2O Power Limited Partnership on the Canadian side) are responsible for maintaining lake level and flow changes from the dams within normal ranges, subject to regulatory oversight by the International Rainy Lake Board of Control (IRLBC). The IRLBC is a board of the International Joint Commission (IJC), which is a bi-national organization created out of the International Boundary Waters Treaty of 1909 for the purposes of handling boundary water issues between the United States and Canada.
Geologically Rainy Lake is part of the Superior Craton of the Canadian Shield and retains features associated with it, such as a large, ancient caldera and fault lines that can be clearly seen in satellite images of the lake.  The Rainy Lake - Seine River Fault zone is a strike-slip fault zone passing through Rainy Lake from Tilson Bay in the southwest to Seine Bay in the northeast.  The Quetico Fault passes through Rainy Lake on an east-west path through McDonald Inlet.  The fault system forms a triangular wrench zone separating the granite-greenstone terrain of the Wabigoon subprovince to the north from the metasedimentary terrain of the Quetico subprovince to the south. 
The rock under the lake and exposed on many of its islands is an exposed part of the North American craton composed of ancient Precambrian rock. This rock has been significantly affected by glaciation, which dominates much of the recent geologic history of the area.
- "Wilder's Edge" by Diane Bradley, published by North Star Press of St. Cloud.
- "Frozen" by Mary Casanova, published by University of Minnesota Press.
- Boundary Waters Canoe Area Wilderness
- Rainy River
- Koochiching County, MN
- Rainy River District, Ontario
- Voyageurs National Park
- Rahm, Joe. Island Images: Rainy Lake’s missing islands. The Journal. 14 Feb. 2010.
- Geographical Place Names of Voyageurs National Park, 2008, retrieved 2013-07-25
- "Rapid Watershed Assessment: Rainy Lake". Natural Resources Conservation Service, U.S. Department of Agriculture. Retrieved 2013-07-25.
- Douglas A. Birk; Jeffrey J. Richner (2004), From Things Left Behind: Fur Trade Sites and Artifacts, Voyageurs National Park and Environs, 2001-2002, Midwest Archeological Center and Institute for Minnesota Archaeology, MAC Technical Report Number 84, IMA Reports of Investigation Number 606
- Ted Catton; Marcia Montgomery, Special History: The Environment and the Fur Trade Experience in Voyageurs National Park, 1730-1870, retrieved 2013-07-25
- Gaultier de Varennes, Pierre (1905), The Canadian West, Montreal: Beauchemin, p. 35, retrieved 2013-12-11
- Gaultier de Varennes, Pierre (1905), The Canadian West, Montreal: Beauchemin, p. 33, retrieved 2013-12-11
- Cary, John (1807), A new map of part of the United States of North America, exhibiting the Western Territory, Kentucky, Pennsylvania, Maryland, Virginia &c., also the lakes Superior, Michigan, Huron, Ontario & Erie; with Upper and Lower Canada &c. From the latest authorities., London: J. Cary, Engraver & Map-seller
- "Border Waters, Your Guide to Northern Minnesota and Northwestern Ontario". International Falls, MN: Border Waters. 2010. Retrieved 2013-07-25.
- Graham, J. (June 2007), Voyageurs National Park Geologic Resource Evaluation Report, Denver, Colorado: National Park Service, U.S. Department of the Interior, Natural Resource Report NPS/NRPC/GRD/NRR—2007/007, retrieved 2013-07-25
- Hemstad, C. B., et al. (2000), M-105 Bedrock geology of the Island View quadrangle, Koochiching County, north-central Minnesota, retrieved 2013-07-25
- Fumerton, S. L. (1982), "Redefinition of the Quetico Fault near Atikokan, Ontario", Canadian Journal of Earth Sciences 19: 222–224
- Poulsen, K. Howard (1986), "Rainy Lake Wrench Zone: An Example of an Archean Subprovince Boundary in Northwestern Ontario", Workshop on Tectonic Evolution of Greenstone Belts