Great Slave Lake 2020 water levels confirmed highest on record

New research confirms Great Slave Lake’s water levels during the summer and fall of 2020 were the highest since monitoring began in the 1930s. 

The Department of Environment and Natural Resources released the findings from a team of hydrological experts on Tuesday. 

The report found precipitation throughout the basins that feed the lake was also the heaviest recorded in at least the past 20 years.


All major rivers feeding into Great Slave Lake had higher than normal water levels as a result.

For example, the Slave River – the largest tributary to the lake – had very high flows due to high levels on the Peace and Athabasca rivers.

Flows were at or near record highs on the Tazin, Taltson, Lockhart, Kakisa, and Hay rivers. 

The territorial government said it was unusual for all of those rivers and lakes to register extremely high water levels at the same time.

The territory previously said high water levels had caused increased sediment in the Hay and Slave rivers last summer. That, in turn, was responsible for the silt cloud observed in Great Slave Lake. Those sediment levels had returned to normal by August and weren’t expected to harm bugs or fish.


According to the territorial government, the latest report concluded that water levels could have been even higher without the influence of the Bennett Dam on the Peace River in British Columbia, which reduced flows on the Peace and Slave rivers. 

The territory said it remains unclear how water levels will change this spring and summer. Levels will depend on the timing and amount of precipitation, ice thickness, and the timing and speed of spring melt. 

Initial research, the report concludes, suggests Great Slave Lake water levels are unlikely to return to normal for some time.