Washington County Lake Quality
Missouri, 2 lakes, average grade C (Fair)
Washington County has 2 graded 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. The county average is C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Lake Shayne-Terre du Lac Lakes (A) is the cleanest in the county.
Quick Answers for Washington County
Planning a trip? Check special fishing regulations for Lake Shayne-Terre du Lac Lakes — or check the official Missouri fishing regulations.
All Lakes in Washington County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Lake Shayne-Terre du Lac Lakes | A | 11.1 ft | 5 µg/L |
| 2 | Sunnen Lake | D | 1 ft | 61 µg/L |
Other Counties in Missouri
See how Washington County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 15 states.
Where to stay near Washington County
Top-rated places to stay near Washington County
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Source: EPA National Aquatic Resource Surveys, 2026.