Mid-Trench Lake
Klamath County, OregonView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Algal growth
- #11 of 17 in the county
Mid-Trench Lake in Klamath County, Oregon has a water quality grade of F (Algae-prone). Phosphorus: 240 µg/L. Chlorophyll-a (algae): 80.6 µg/L.
- Type
- Hypereutrophic
- Phosphorus
- 240 µg/L
- Chlorophyll-a
- 80.6 µg/L
- Trend
- ↑ Improving
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Stays near Mid-Trench Lake
Compare lakeside cabins, hotels, and vacation rentals near Mid-Trench Lake in Klamath 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Mid-Trench Lake are listed below.
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Mid-Trench Lake is a highly nutrient-loaded hypereutrophic lake in Klamath County, Oregon. Water quality is graded F based on 2 sampling years through 2023. Overall water quality is improving over recent sampling years. Compared to the 16 other monitored lakes in Klamath County, Mid-Trench Lake ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Oregon DEQ, last sampled 2023-09-25. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The F is nutrients and algae, not a swimming clearance. Mid-Trench Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, mercury, oxygen depletion (low DO), pH / acidity, sediment / turbidity, temperature. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
No clarity data. Phosphorus 240 µg/L. Chlorophyll-a 80.6 µg/L. TSI 78. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 240 µg/L | Poor |
| Chlorophyll-a (Algae) | 80.6 µg/L | Poor |
| Trophic State Index (TSI) | 78 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Fishing Mid-Trench Lake
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↑ Improving | -22 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -27.81 µg/L/yr | 4 |
EPA Impairment Status
Mid-Trench Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit OR_LK_1801020303_05_100375 · Official waterbody report · Matched by proximity (2.61 km)
County Ranking
Ranked #11 of 17 lakes in Klamath County
Nearby Lakes in Klamath County
Frequently asked questions about Mid-Trench Lake
Where is Mid-Trench Lake?
- Mid-Trench Lake is a lake in Klamath County, Oregon. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Mid-Trench Lake?
- Mid-Trench Lake in Klamath County, Oregon has a water quality grade of F (Algae-prone). Phosphorus: 240 µg/L. Chlorophyll-a (algae): 80.6 µg/L.
Is Mid-Trench Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Mid-Trench Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, mercury, oxygen depletion (low DO), pH / acidity, sediment / turbidity, temperature. Check local advisories before you swim.
Explore Mid-Trench Lake across LakeQuality
4 thermal springs within 21.8 mi, nearest Howard Holiday
Species activity outlook by water temperature and season
Where to stay at Oregon's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
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Other Grade F Lakes in Oregon
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Where this data comes from
83 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Oregon Water Science Center
USGS-OR83 samples · 2020–2023
Analytical methods
- Nutrients, wu, WCA,persulfate,CF
- Chlorophyll a, phytoplankton
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database