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LakeQuality
Late afternoon sun over Slim Lake, scattering a bright path across wind-textured water
F

Union County Lake Quality

Oregon, 13 lakes, average grade F (Algae-prone)

Union County holds 13 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. 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 Thief Valley Reservoir (F); the most-stressed is Thief Valley Reservoir (F).

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All Lakes in Union County

13 lakes · 1 graded, 12 not rated1 graded lake · 12 not rated, hidden

#LakeGradeClarityPhosphorusAlgaeTrophicAccess
1FThief Valley ReservoirUnionFNo recent samplesNo recent samples51.2 µg/LNo recent samples✓ Public
NRMorgan LakeUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samples✓ Public
NRConley LakeUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRJubilee LakeUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samples✓ Public
NREagle LakeUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRGlacier LakeUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRLookingglass LakeUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NREcho LakeUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRFisk ReservoirUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRLa Grande ReservoirUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRShaw ReservoirUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRWolf Creek ReservoirUnionNRNo recent samplesNo recent samplesNo recent samplesNo recent samples✓ Public
NRPilcher Creek ReservoirUnionNRNo recent samplesNo recent samplesNo recent samplesNo 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.

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Source: EPA National Aquatic Resource Surveys, 2026.