Washington County Lake Quality
Oregon, 3 lakes, average grade A (Excellent)
Washington County holds 3 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 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 an A. That puts it near the top of the Oregon county ranking.
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. Henry Hagg Lake (A) is the cleanest in the county.
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Quick Answers for Washington County
Planning a trip? Check special fishing regulations for Henry Hagg Lake — or check the official Oregon 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 | AHenry Hagg LakeWashington | A | No recent samples | No recent samples | 1.5 µg/L | No recent samples | ✓ Public |
| NRStimson MillpondWashington | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRBarney ReservoirWashington | 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.
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Other Counties in Oregon
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.