Special thanks to Dr. Stephen Jacquemin, Professor of Biology, Wright State University-Lake Campus, for providing data, context and insights for this report.

Current microcystin levels are higher than they were the past two years, but they’re still below historical averages, suggesting that ongoing conservation efforts are having a positive impact on Grand Lake St. Marys water quality.

The current average is around 20 ug/L, higher than 2022’s average of 11 ug/L and 2021’s average of 1.5 ug/L.

However, current levels are still lower than during the years preceding 2021. From 2018-2020, spring averages were around 28 ug/L. From 2014-2017, they ranged from 40 to 90 ug/L.

Average Microcystin Levels (ug/L)
Spring 2023 20
Spring 2022 11
Spring 2021 1.5
Spring 2018-2020 28
Spring 2014-2017 40 to 90

The current average will likely increase a bit with additional weeks of elevated microcystin levels, but our spring values are still not tracking the highest years from the past.

Complex factors influence microcystin levels

There is a complex network of factors that contribute to microcystin values. Recent studies on Grand Lake St. Marys have indicated a combination of ice cover coupled with early spring runoff contribute strongly to spring bloom formation. What we are seeing this year is, at least in part, a result of low ice cover (milder winter) coupled with high runoff rates driven by a few precipitation events.

What it means for early summer 2023

The values will likely trend upward over the next month, at which point they should come down a bit. This projection is based on over a decade of historical data. Every year is different, of course, but this is what the long-term data indicates.

Year over year trends strongly suggest that our collective efforts are having a significant, positive impact on water quality

Despite the current spike, the long-term data also tells us that our peak period this year will likely pale in comparison to peak periods in past years, indicating a degree of conservation progress.

Still, the current data illustrates that more work needs to be done. In particular, the emphasis on conservation practices around the watershed helps to reduce spring loading and lessen bloom intensity by keeping nutrients out of the system.

The goal is a safe, clean and healthy lake no matter the weather. To achieve that, we need the community’s continued support for our ongoing efforts to restore Grand Lake St. Marys.