Advisory for JACKFISH LAKE, Northwest Territories

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JACKFISH LAKE

Type: Cyanobacteria Bloom  -  Active

Issued: 6/19/2025

Details:

JACKFISH LAKE (Yellowknife) – June 19 Residents are reminded that the Lake remains unsafe for swimming, fishing or other recreational use due to elevated levels of arsenic and harmful algae. 

Since 2013, cyanobacteria, commonly known as blue-green algae, has been monitored in Jackfish Lake; Cyanobacteria is present in Jackfish Lake at all times of the year. The high concentrations of cyanobacteria have been attributed to the combination of physical characteristics of the lake and historical environmental impacts of nearby land uses.

Historical evidence has shown that the Northwest Territories Power Corporation’s (NTPC) operation of the Jackfish Lake Power Generation Facility (power plant) is not solely responsible for the proliferation of cyanobacteria in Jackfish Lake. Surrounding land use, including the Yellowknife landfill site, road networks, and cemetery, are also likely contributing nutrients to the lake.

In the Yellowknife area, arsenic levels are naturally higher than in other places, due to the local geology. However, historical gold mining activities, particularly in the Yellowknife area, have released large amounts of additional arsenic into the environment.

Spring 2016 N.W.T. health official to release advisory on arsenic levels in Yellowknife lakes following a recent study, released by the University of Ottawa, that found arsenic concentrations higher than the Canadian Drinking Water Guidelines in lakes within 15 km of the shuttered Giant Mine. During the 50 years the Giant Gold Mine operated, it is estimated that 20,000 tonnes of highly toxic dust (arsenic trioxide) spewed from the stack and settled on the ground and lakes around Yellowknife; this area is referred to as the Area of Concern.

Under the Public Health Advisory issued for the Area of Concern and surround, residents and visitors are instructed to:
•	Do not consume the water.
•	Do not swim or wade.
•	Do not fish.
•	Do not pick berries, harvest garden vegetables or other edible plants within the Area of Concern (the approximate footprint of settled arsenic dust).
•	Do not consume mushrooms picked within 10 km radius of Giant Mine.
•	Mushrooms harvested within 10 km to 25 km pose a very low risk from arsenic exposure if consumed; however, mushrooms from the Tricholomataceae family (e.g. Tricholoma, Clitocybe, White Matsutake) should not be consumed if picked within 25 km radius of Giant Mine.

The following list of lakes, noted with their Dissolved Arsenic Concentration, are located within 10 km radius of Giant Mine and have been deemed unsafe for consumption, swimming and fishing:

David Lake	213.0 µg/L
Fox Lake	241.0 µg/L
Frame Lake	212.5 µg/L
Gar Lake	97.7 µg/L
Handle Lake	140.0 µg/L
Jackfish Lake	91.7 µg/L
Kam Lake	238.0 µg/L
Peg Lake	638.0 µg/L
Pocket Lake	2,240.0 µg/L
Meg Lake	67.0 µg/L
Rat Lake	197.0 µg/L