Great Slave Lake Water Resources: Using Earth Observations to Monitor Water Quality of Great Slave Lake in the Northwest Territories, Canada

Great Slave Lake in Canada’s Northwest Territories (NWT) is a vital freshwater resource that supports local fisheries and tourism. Recent increases in sediment concentrations from the Slave River affect Great Slave Lake’s water quality. The Government of the NWT (GWNT) Water Research and Monitoring Section collects in situ water quality data, but due to limited resources they lack large-scale spatial and temporal insights into turbidity patterns. To address these challenges, we developed turbidity algorithms using in situ turbidity and reflectance data. We then applied these algorithms to imagery from NASA’s Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), European Space Agency’s Ocean Colour Climate Change Initiative (OC-CCI), and Sentinel-3A Ocean Land Color Instrument to assess the feasibility of using the shorter-wavelength sensors (MODIS and OC-CCI)for turbidity monitoring over longtime scales. Using OC-CCI, we constructed a time series of monthly average turbidity from June to October, 2002to 2024 for Great Slave Lake and five sub-sections: North Finger, North Mid-Arm, Central Basin, South Basin, and East Arm. We also analyzed the seasonality of turbidity and its relationship with Slave River discharge. To validate algorithms, we compared in situ turbidity measurements to Sentinel-2 Multispectral Imager (MSI) derived values. The results suggest OC-CCI is feasible for measuring turbidity. There were no observable long-term turbidity trends in Great Slave Lake, but turbidity was highest in the North Finger and lowest in the East Arm, with noticeable spikes in 2011 and 2020. Great Slave Lake turbidity was not significantly influenced by Slave River discharge. Despite limitations, our approach offers a cost-effective, scalable solution for improving water resource management in Great Slave Lake.