Current & Historical Microcystin Levels in Grand Lake St. Marys

* Current numbers are averages. Microcystin levels vary at different lake locations. Courtesy Dr. Stephen Jacquemin, Wright State University-Lake Campus

Frequently Asked Questions

Micrograms per liter.

Parts per billion, or ppb, represents the amount of microcystin in a billion parts of water. In other words, it is the concentration of microcystin. The conversion of ppb to ug/L is 1:1, which means that 10ppb = 10 ug/L. Essentially, it’s two different ways to say the same thing.

The World Health Organization says water is safe to swim in at or under 20 ug/L. However, the State of Ohio puts the threshold at 8 ug/L. 

Helpful links include:


LIA Knowledge Base

For more information, contact the Grand Lake St. Marys State Park Office at 419-394-3611.