Washington County Lake Quality

Washington County has 9 monitored lakes — 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. 1 of those lake carry recent nutrient and algae readings. The county-level summary describes that subset, not every water body listed. On average, Washington County lakes carry some of the lowest phosphorus and chlorophyll-a readings in Missouri, 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 measured lake is Lake Shayne-Terre du Lac Lakes.