[2] The lake is in the Grenville Province in the southeast of the Canadian Shield plateau, composed of Precambrian rocks, on average 300 metres (980 ft) above sea level.

[citation needed] Carheil Lake is at the head of the Moisie River drainage basin, and drains an area of 328 square kilometres (127 sq mi).

[2] A measurement of lake temperature in late July 2011 gave 16 °C (61 °F) near the surface, falling to 5 °C (41 °F) at the lowest levels.

[12] A map of the Ecological regions of Quebec shows the Carheil Lake rising to the south of Fermont just west of the Spruce/lichen domain of the boreal zone.

[18] A new 6 kilometres (3.7 mi) quad (all-terrain vehicle) trail was built in 2015 from Fermont to the lake by the Club VTT du Grand Nord.

[15] In 2017 Metals Australia announced initial exploration results at their 4,450 hectares (11,000 acres) Lac Rainy Est graphite project, important in providing an input to lithium-ion battery manufacturing.

[22] A report by the same company in May 2019 stated that they had drilled 17 holes along the formation for a length of about 1.25 kilometres (0.78 mi) and confirmed eastern and western extensions of the Carheil Graphitic Zone.

[24] In April 2011 it was reported that water management experts in Sept-Îles were concerned about cyanobacteria, or blue-green algae, that had been found in Carheil Lake.

The cause of excessive phosphorus in the lake was discharge from the Fermont treatment plant over a period of forty years.

[25] The Ministry of Sustainable Development, Environment and Parks (MDDEP) told the OBV Duplessis to evaluate the situation of Carheil Lake, resulting in publication of a study in November 2011.

The report noted that Lakes Daviault and Sans-Nom had also been affected with cyanobacterial efflorescence every year since 2005, and the Fermont treatment plant was the only known source of phosphorus.

Almost the only information available was on the water quality in 1996 at the mouth of the Moisie River, 350 kilometres (220 mi) downstream.

[29] By comparison, Lake Perchard, to the north of Fermont, supplies the town with drinking water.