Mercer County Lake Quality

Mercer County has 1 monitored lake — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. Every one of those lake carries recent nutrient and algae readings, so the county-level summary covers the full set rather than a monitored subset. The monitored lakes here are mostly shallow, productive basins where summer algae is common; each lake page shows its own readings beside the EPA condition class.

The county's lakes lean shallow, which makes the readings sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the readings is Grand Lake St Marys @ Intake.