[2] The Sainte-Marguerite River enters the Gulf of Saint Lawrence about 30 kilometres (19 mi) by road west of Sept-Îles.

[4] During the Holocene the Sainte-Marguerite created a delta of thick paraglacial and post-glacial sediments that completely cover the glacial landforms and glaciomarine deposits near the river mouth.

[6] The river mouth today is a haven for small boats during bad weather in the Gulf, because the basin that it forms is protected by the Pointe Sainte-Marguerite.

[2] The name was used as early as 1603, when Samuel de Champlain wrote, "we came to anchor near a river called Saincte Marguerite".

[2] A map of the Ecological regions of Quebec shows the river rising and flowing south through the eastern spruce/moss domain of the boreal zone.

The project was managed in 1991–1998 by Cérane (Centre d’étude et de recherche en archéologie du Nord-Est).

[8] The oldest known site on the Sainte-Marguerite is found on the portage, a temporary halt where hunters took the time to cut or sharpen spear points about 4,000 years ago.

Another site along the Grand Portage is on the north shore of Lac Jourdain (map), containing 11 structures with 61 stone tools and over 7,000 shards.

[9] A site on the upper river dating to between 600 and 1000 years ago indicates that the occupants caught fish and smoked their catch there.

A prehistoric site of about 350 square metres (3,800 sq ft) has been identified on the flat right shore of the Rivière Jean-Pierre, at the extreme northeast of the SM-3 reservoir.

The train was owned by the North Shore Power Railway & Navigation Company, founded by the Clarke Brothers in 1902.

The river flow is regulated by the SM-3 generating station and reservoir 70 kilometres (43 mi) upstream, which came into service in Spring 2003.

[14] The plant was acquired by Innergex (50.1%) and Desjardins Group Pension Plan (49.99%) in 2014, and delivers power under contract to Hydro Quebec.

[18] Another side effect, which had been anticipated, was a rise in mercury levels by factors of 6 to 8 in lake whitefish (Coregonus clupeaformis) and northern pike (Esox lucius), the main species of fish in the reservoir.

Brook trout (Salvelinus fontinalis), the preferred fish for the local people, tend to avoid large reservoirs and were not affected.