Bacteria in freshwaters can pose a human health risk if present in high levels, potentially causing a variety of diseases. Bacteria can enter water bodies from point and nonpoint sources and are particularly problematic following storms. This indicator assesses Escherichia coli (E. coli) in the water during the summer season (May 1st–September 30th), when recreation is highest, against the Michigan Department of Environment, Great Lakes, and Energy’s threshold.
How is it scored?
The geometric mean was calculated from each sampling station using the most recent sampling year available, which ranged from 2019 to 2021 depending on the station. Stations were scored pass/fail based on the threshold of 130 per 100 mL. Station scores were averaged to calculate the watershed score. Watershed scores were population-weighted to calculate the overall region score.
Data source: Data from 2015 to 2022 were downloaded from the National Water Quality Monitoring Council’s data portal (https://www.waterqualitydata.us/).