Union County Lake Quality

Union County holds 1 monitored lake. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 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. On average, Union County lakes carry some of the lowest phosphorus and chlorophyll-a readings in Ohio, with clear summer transparency across most monitored basins.

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 Marysville Upground Reservoir.