Twentymile Slough
Twentymile Slough in Lake County, Oregon is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 419 acres.
- Area
- 419 acres
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Why Twentymile Slough has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Twentymile Slough, no water-quality sampling on record for this lake.
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by Oregon DEQ and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Twentymile Slough is a 419-acre lake in Lake County, Oregon.
Source: EPA Water Quality Portal sampling records, Oregon DEQ, last sampled recent years. Grade methodology: LakeQuality methodology.
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Swimming Safety
Not ratedElevated nutrients
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Twentymile Slough
These readings exist but are not enough for an A–F grade — see why.
No clarity data. Trophic State Index: undefined.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) |
Where to stay near Twentymile Slough
Compare lakeside cabins, hotels, and vacation rentals near Twentymile Slough in Lake County, Oregon — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 419 acres |
No bathymetric survey has been published for Twentymile Slough, so its depth is not documented here.
Fishing Twentymile Slough
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Frequently asked questions about Twentymile Slough
Where is Twentymile Slough?
- Twentymile Slough is a lake in Lake County, Oregon. LakeQuality has not rated this lake (UNRATED) — no water-quality sampling on record for this lake.
What is the water quality grade for Twentymile Slough?
- Twentymile Slough in Lake County, Oregon is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 419 acres.
Is Twentymile Slough safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Twentymile Slough is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
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Where this data comes from
Measurements for Twentymile Slough come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.