Recent tests by the Celina Water Treatment Plant indicate that microcystin levels in Grand Lake St. Marys are the lowest they’ve been since 2011 and 2012, when levels dipped after the lake was treated with alum. Current microcystin levels are between 25 and 35 parts per billion (ppb), a significant decrease from the 75+ ppb detected in recent years. The World Health Organization’s “no contact advisory” threshold is 20 ppb.
Using figures provided by the Celina Water Treatment Plant, Wright State University Biology and Research Coordinator Dr. Stephen Jacquemin compiled the below graphic. It depicts seasonal microcystin levels in Grand Lake St. Marys from 2009 to 2019. Though levels clearly fluctuate, the fact that microcystin levels are the lowest they’ve been since the 2011 alum treatment suggests that water quality improvement efforts are having a positive impact on the lake. The Lake Improvement Association is encouraged by the figures, but stresses more work needs to be done to bring microcystin to safe levels in Grand Lake St. Marys.