Lake Nipigon ( ; ; ) is part of the Great Lakes drainage basin. It is the largest lake entirely within the boundaries of the Canadian province of Ontario.
Etymology
In the Jesuit Relations the lake is called lac Alimibeg, and was subsequently known as Alemipigon or Alepigon. In the 19th century it was frequently spelled as Lake Nepigon. This may have originated from the Ojibwe word Animbiigoong, meaning 'at continuous water' or 'at waters that extend [over the horizon].' Though some sources claim the name may also be translated as 'deep, clear water,' this description is for Lake Temagami. Today, the Ojibwa bands call Lake Nipigon Animbiigoo-zaaga'igan.
The 1778 Il Paese de' Selvaggi Outauacesi, e Kilistinesi Intorno al Lago Superiore map by John Mitchell identifies the lake as Lago Nepigon and its outlet as F. Nempissaki. In the 1807 map A New Map of Upper & Lower Canada by John Cary, the lake was called Lake St Ann or Winnimpig, while the outflowing river as Red Stone R. Today, the Red Rock First Nation located along the Nipigon River still bears the "Red Stone" name. In the 1827 map Partie de la Nouvelle Bretagne. by Philippe Vandermaelen, the lake was called L. Ste Anne, while the outflowing river as R. Nipigeon. In the 1832 map North America sheet IV. Lake Superior. by the Society for the Diffusion of Useful Knowledge, the lake was called St Ann or Red L., while the outflowing river as Neepigeon and the heights near the outlet of the Gull River as Neepigon Ho. By 1883, maps such as Statistical & General Map of Canada by Letts, Son & Co., consistently began identify the lake as Lake Nipigon.
Geography
Lying 260 metres (853 ft) above sea level, the lake drains into the Nipigon River and thence into Nipigon Bay of Lake Superior. The lake and river are the largest tributaries of Lake Superior. It lies about northeast of the city of Thunder Bay, Ontario.
Lake Nipigon has a total area (including islands within the lake) of , compared to for Lake of the Woods. It is the 32nd largest lake in the world by area. The largest islands are Caribou Island, Geikie Island, Katatota Island, Kelvin Island, Logan Island, Murchison Island, Murray Island, and Shakespeare Island. Maximum depth is .
Its original watershed area is . This was increased by about 60% to after of the Ogoki River basin were diverted in 1943 to the headwaters of the Little Jackfish River, a tributary of Lake Nipigon.
Geology
Lake Nipigon occupies a basin created by repeated and preferential erosion of relatively flat-lying and faulted, Proterozoic sedimentary strata and igneous sills by repeated Pleistocene glaciations. The Sibley Group consists of about of unmetamorphosed Mesoproterozoic red beds that are typically flat-lying. These red beds consist of basal fluvial-lacustrine conglomerates, sandstones, and shales overlain by cyclic dolomite-siltstone layers, stromatolites and red mudstones, which represent a playa lake, sabkha, and mudflat environments; purple shales and siltstones interpreted as subaerial mudflat deposits; and an upper unit of cross-stratified sandstone beds, which are interpreted to be aeolian in origin. They accumulated in an intracratonic rift basin between 1450 and 1500 million years (Ma) ago.
The Sibley Group unconformably overlies highly deformed and metamorphosed Archean turbiditic sandstones and metavolcanic and granitic rocks. The strata of the Sibley Group fill and are limited to a rift basin known as the Nipigon Embayment that underlies Lake Nipigon. Outside of the rift basin and east and west of Lake Nipigon, the Sibley Group is absent and erosion resistant Archean rocks are either exposed at the surface or blanketed by Pleistocene glacial sediments.
The Archean and Proterozoic strata are intruded by a number of mafic and ultramafic intrusions, which define the current outline of the Nipigon Embayment. They consist of relatively flat-lying and undeformed diabase sills known as the Nipigon diabase sills. These sills range in thickness from a few meters to thick in cliff sections to more than thick in drill core. They are estimated to cover an area in excess of . The Nipigon diabase sills give evidence of rift-related continental basaltic magmatism during the Midcontinent Rift System event, estimated at 1,109 Ma ago. Thick sills up to thick are also related with the rifting event, forming cliffs that are up to high. The mafic and ultramafic intrusions centered on Lake Nipigon is interpreted to represent a failed arm of the Nipigon embayment.