Caniapiscau Reservoir is a man-made lake, created as part of the La Grande Complex (James Bay) Hydro-electric Project. The reservoir incorporates several large lakes, (Delorme, Brisay, Tournon, and Vermouille) which were present before reservoir formation. Lake Caniapiscau, located at the eastern end of the complex, catches 40% of the headstream of Caniapiscau River which formerly drained into the Koksoak River and into Ungava Bay. The impoundment was initiated in October 1981. Since August 1985, waters from the Caniapiscau Reservoir were diverted toward the La Grande 4 Reservoir and thence to LG3 and LG2 Reservoirs and to James Bay.

The Caniapiscau Reservoir was constructed by Societe d'Energie de la Baie James, a crown corporation of the Province of Quebec (now a subsidiary of Hydro Quebec) as part of a $16 billion (Can. $) development project called La Grande Complex Phase 1. It regularizes on an annual and interannual basis the whole complex (1) and produces 10,300 megawatts of electricity. The electricity is transported in 5 high voltage lines which are supported by 12,000 hydroelectric transmission towers spread over the longest high voltage transmission system in North America (12).

There is no human habitation near the reservoir. In the past, the area was used for hunting by Cree Amerindian people of the area. Some hunting, trapping and fishing is still carried out in the area by Cree people who travel by road from the town of Chisasibi. As well, there are some outfitting operations (none with permanent structures) for hunting (mainly caribou) and fishing (mainly by tourists).