Summary of Assessment
Moderate changes to aquatic ecosystem health have occurred in the Great Slave sub-basin, according to most indicators considered in the assessment. Observed changes were mainly related to climate change, upstream regulation of river flows, contamination from mining activities and overharvest of fish stocks.
Water Quantity
- Lower water levels in the Slave Delta and rivers in the southern portion of the sub-basin.
- Significant expansion of lake surface areas and associated increases in river flows west of Great Slave Lake, related to climate change.
- Increases in winter air temperatures and variable precipitation.
Habitat & Species
- Declines in fish populations and fish health condition, the former linked historically to commercial fisheries in Great Slave Lake.
- Measured contaminant levels in fish are safe for consumption, except in specific water bodies contaminated by active and abandoned mines.
Water Quality
- Increase in sediment and contaminants in the water and warmer surface water temperatures, as reported by Indigenous communities, but not in scientific data.
Health & Wellbeing
- Less consumption of fish, muskrat and other country foods, due to reduced access, concerns for contamination, and some severely reduced fish stocks.
- Access to preferred fishing sites and harvesting areas is reduced due to lower water levels such as in the Mackenzie River, Slave River and Slave River Delta.
Water Quantity
- Lower water levels in the Slave Delta and rivers in the southern portion of the sub-basin.
- Significant expansion of lake surface areas and associated increases in river flows west of Great Slave Lake, related to climate change.
- Increases in winter air temperatures and variable precipitation.
Water Quality
- Increase in sediment and contaminants in the water and warmer surface water temperatures, as reported by Indigenous communities, but not in scientific data.
Habitat & Species
- Declines in fish populations and fish health condition, the former linked historically to commercial fisheries in Great Slave Lake.
- Measured contaminant levels in fish are safe for consumption, except in specific water bodies contaminated by active and abandoned mines.
Health & Wellbeing
- Less consumption of fish, muskrat and other country foods, due to reduced access, concerns for contamination, and some severely reduced fish stocks.
- Access to preferred fishing sites and harvesting areas is reduced due to lower water levels such as in the Mackenzie River, Slave River and Slave River Delta.
People & Places
The Great Slave sub-basin is sparsely populated with settlements primarily situated along the shores of Great Slave Lake. The sub-basin overlaps with the traditional territories of at least five Indigenous groups. The lands of the Akaitcho and Tlicho are north of Great Slave Lake, with settlements located at Gamèti, Wekweètì, Whatì, and Behchoko. The Dehcho region is located west of Great Slave Lake and spans the territories of Dehcho First Nations, with settlements located at Wrigley, Fort Simpson, Jean Marie River, Kakisa, Sambaa K’e, Hay River, and Fort Providence. To the south are the lands of the Akaitcho, Northwest Territories Métis Nation and Denesuline, with communities located at Fort Resolution, Fort Smith and Lutsel K’e.
Water quantity in the Great Slave sub-basin has undergone moderate change. Observations by Indigenous communities and scientists suggest that ice is less thick and unstable in some areas, with earlier break-ups and later freeze-up dates in many waterbodies, including the Slave River and Slave River Delta. Scientific assessments indicate snow mass has decreased since 1980 over much of the northern and southern portions of the sub-basin, while observations by Indigenous communities suggest changes in snow texture and quality. Water levels in lakes, rivers, and creeks are more variable than in the past, notably in the Horn River and the Slave River Delta. Flows are generally lower than in the past in the Slave, Taltson and Mackenzie Rivers. These changes are largely the result of a combination of flow regulation on the Peace River by the W.A.C. Bennett Dam and the effects of climate change. In contrast, flows in rivers west and northwest of Great Slave Lake have increased, along with significant expansion of lake surface areas, related to climate change. These changes in water quantity threaten to further disrupt the aquatic ecosystem health and the ability for Indigenous communities to practice a traditional way of life in the sub-basin.
Read more about Snow & Ice, Water Flows & Levels, Climate and Water Use
Moderate changes in water quality have been observed in the Great Slave sub-basin. Some Indigenous communities have observed an increase in sediment in the water, warmer surface water temperatures, and more lesions and parasites in fish. Scientific studies indicate elevated levels of some heavy metals in the Slave River, including mercury and aluminum, but have not detected trends, and thus have attributed levels to naturally elevated sediment loads. High turbidity has been reported in water flowing into Great Slave Lake from the Marian and Slave Rivers, and significant increasing trends in ionic strength (salts) and spring temperatures were recorded in several rivers throughout the sub-basin suggesting a broader regional influence. The sub-basin is not densely populated with human settlements and effluent volumes remain minimal. However, human activity linked to mining, forestry and other industries has increased over time, in particular the Hay River watershed. Significant concerns among Indigenous communities remain for how contaminants from industrial development activities affect water quality and ecosystem health.
Read more about Water Quality, Benthic Invertebrates, Land Use and Effluent Discharges
Aquatic habitat and species in the Great Slave sub-basin are undergoing moderate change. Unhealthy fish with physical deformities and softer flesh and mass fish die-offs have been observed by many Indigenous communities. Populations of some fish species are declining, such as grayling (Thymallus arcticus) and suckers (Catostomus spp.) in the Mackenzie River, and coney (Stenodus leucichthys) stocks near Yellowknife. Mercury and arsenic contamination affect fish populations in certain waterbodies near historical mine sites; however, in most places scientific data show that fish are safe to eat. Indigenous communities have reported new fish species rarely or never seen in the sub-basin, such as coney near Lutselk’e and salmon near Yellowknife. Documented scientific or Indigenous Knowledge observations of changes in wetland cover and riparian forests in the sub-basin are limited. However, some Indigenous communities have observed changes in wetland-dependent animal populations, particularly more variability in beaver (Castor canadensis) populations and a continued decline in muskrat (Ondatra zibethicus) abundance.
Changes in aquatic ecosystem health have moderate impacts on the health and wellbeing of Indigenous communities in the Great Slave sub-basin. The inclusion of country (or traditional) foods in local diets is viewed as essential to many Indigenous communities because of the nutritional, cultural, and spiritual values linked to these resources. Although fishing, hunting, trapping, and gathering country foods are still viewed as core cultural practices, many Indigenous communities in the sub-basin report consuming less fish than in the past due to many factors, particularly out of concern for elevated levels of mercury, arsenic and other toxins in certain waterbodies and fish populations. Access to preferred fishing sites and harvesting areas is also becoming more difficult and dangerous due to lower water levels such as in the Mackenzie River, Slave River and Slave River Delta. No scientific data was found for levels of country food consumption in the Great Slave sub-basin.
