Malheur Lake
Harney County, OregonView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Algal growth
- #1 of 1 in the county
- 91 ft max depth
Malheur Lake in Harney County, Oregon has a water quality grade of F (Algae-prone). Phosphorus: 460.5 µg/L. Chlorophyll-a (algae): 45.5 µg/L.
- Max depth
- ~91 ft est.
- Type
- Hypereutrophic
- Phosphorus
- 460.5 µg/L
- Chlorophyll-a
- 45.5 µg/L
- Trend
- → Stable
Stays via Stay22
Stays near Malheur Lake
Compare lakeside cabins, hotels, and vacation rentals near Malheur Lake in Harney 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 Malheur Lake are listed below.
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Malheur Lake is a highly nutrient-loaded hypereutrophic lake in Harney County, Oregon with an estimated average depth of about 91 feet. Water quality is graded F based on 2 sampling years through 2023. Phosphorus level is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, Oregon DEQ, last sampled 2023-10-19. 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. Malheur Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
No clarity data. Phosphorus 460.5 µg/L. Chlorophyll-a 45.5 µg/L. TSI 80. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 460.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 45.5 µg/L | Poor |
| Trophic State Index (TSI) | 80 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~91 ft est. |
| Average Depth | ~8 ft est. |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Oregon has not published bathymetry for Malheur Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Malheur Lake
Water Quality Trend: → Stable
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +196.5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -22.25 µg/L/yr | 2 |
EPA Impairment Status
Malheur Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit OR_LK_1712000107_09_100912 · Official waterbody report · Matched by proximity (2.64 km)
County Ranking
Ranked #1 of 1 lakes in Harney County
Nearby Lakes in Harney County
Frequently asked questions about Malheur Lake
Where is Malheur Lake?
- Malheur Lake is a lake in Harney County, Oregon. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Malheur Lake?
- Malheur Lake in Harney County, Oregon has a water quality grade of F (Algae-prone). Phosphorus: 460.5 µg/L. Chlorophyll-a (algae): 45.5 µg/L.
Is Malheur Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Malheur Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth. Check local advisories before you swim.
How deep is Malheur Lake?
- No published bathymetric survey covers Malheur Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 91 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Malheur Lake across LakeQuality
3 thermal springs within 16.9 mi, nearest Dunn Spring
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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Where this data comes from
245 measurements from 13 monitoring stations, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Oregon Water Science Center
USGS-OR245 samples · 2020–2023
Analytical methods
- P, wu, WCA, persulfate CF color
- YSI 6025, 470/685 nm, Isochrysis
- Plant pigments, sonication & 445
- YSI Environmental, sensor 6136
Monitoring station identifiers (13)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)