Washington County Lake Quality
Iowa, 2 lakes, average grade F (Algae-prone)
Washington County has 2 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 an A–F grade. The county-level summary describes that subset, not every water body listed. The county average is F — the most-stressed bracket in our rubric. Most monitored lakes here show persistent nutrient loading and algal pressure.
The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is Lake Darling Max Depth (F); the most-stressed is Lake Darling Max Depth (F).
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Quick Answers for Washington County
Planning a trip? Check special fishing regulations for Lake Darling Max Depth — or check the official Iowa fishing regulations.
All Lakes in Washington County
2 lakes · 1 graded, 1 not rated1 graded lake · 1 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | FLake Darling Max DepthWashington | F | 1.6 ft | 226 µg/L | 60.5 µg/L | No recent samples | ✓ Public |
| NRLake Darling BeachWashington | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public |
NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
Lake Match
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Other Counties in Iowa
See how Washington County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..
Source: EPA National Aquatic Resource Surveys, 2026.