Washington County Lake Quality
Oklahoma, 3 lakes, average grade D (Nutrient-rich)
Washington County has 3 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. On average, Washington County lakes grade D, with phosphorus loading and reduced clarity showing up across most of the dataset.
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 Copan Lake (D); the most-stressed is Copan Lake (D).
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Quick Answers for Washington County
Planning a trip? Check special fishing regulations for Copan Lake — or check the official Oklahoma fishing regulations.
All Lakes in Washington County
3 lakes · 1 graded, 2 not rated1 graded lake · 2 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | DCopan LakeWashington | D | 1.6 ft | 79 µg/L | No recent samples | No recent samples | ✓ Public |
| NRYoungs LakeWashington | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRLong LakeWashington | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded |
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
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Other Counties in Oklahoma
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.