A comprehensive suite of remote sensing algal bloom indices for enhanced monitoring of Canadian eutrophic lakes.

There is substantial evidence that the frequency and magnitude of harmful algal blooms (HABs) in coastal and inland waters around the world have been increasing. Often, however, the lack of consistent lake-wide and long term in situ datasets on HABs impedes our ability to resolve their short and long term variance and develop robust management strategies for mitigating their impact. Earth observation satellites are increasingly being used to deliver quantitative measures of inland water algal blooms. We will present satellite derived indices for algal bloom intensity, spatial extent, severity, and duration, for three shallow lakes in Canada which experience annual, often severe, algal blooms; Lake Winnipeg, Lake Erie, and Lake of the Woods. Chlorophyll concentrations and subsequent bloom indices are derived using the Maximum Chlorophyll Index, a line-height algorithm targeting the peak in reflectance in the 708nm band available on the European Space Agency (ESA)'s Sentinel-3A OLCI and its predecessor Envisat MERIS. Results will be presented on the derivation of these bloom indices and their validation against in situ observations. These satellite derived algal bloom indices are now used operationally by Environment and Climate Change Canada to provide objective, consistent measures of algal bloom conditions that are vital for large scale assessments of lake health, change detection, and setting targets for lake management actions. Time series of bloom conditions on each lake are analysed with respect to known climate and watershed drivers of algal blooms in order to further understand the seasonal and inter-annual variability in bloom timing and severity.