Why did NOAA recalculate the historic time series record of Lake Erie harmful algal bloom severity in 2025?

• Recent advances in satellite technology give scientists a much clearer picture of what’s happening with harmful algal blooms in large bodies of water like Lake Erie. Modern satellites provide imagery nearly daily and at nine times the spatial resolution as before. They can more accurately detect and quantify the amount of cyanobacteria present in the water.
• Over the past decade, NOAA has been working to update their algal bloom detection methods and merge datasets from multiple satellites. The last complete reprocessing was done in 2015. The Sentinel-3 satellite, NOAA’s current (and future) reference was launched in 2016. NOAA used the higher quality satellite imagery available since 2016 to recalculate the time series and fill gaps in the historic record.
• This was a significant undertaking that was years in the making to ensure NOAA continues to use the best available science to assess Lake Erie’s harmful algal blooms.