Diamond Lake is a productive, nutrient-rich eutrophic lake in Douglas County, Oregon. Water quality is graded F based on 1 sampling years through 2025. Compared to the 2 other monitored lakes in Douglas County, Diamond Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Oregon DNR, last sampled 2025-09-24. Grade methodology: LakeGrade methodology.
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
No clarity data. Chlorophyll-a: 42.6 µg/L. Trophic State Index: 67.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 42.6 µg/L | F |
| Trophic State Index (TSI) | 67 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Diamond Lake
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Fishing Diamond Lake
Location
County Ranking
Ranked #3 of 3 lakes in Douglas County
Cleaner Lakes Within 30 Miles
Diamond Lake holds Grade F. 2 nearby lakes hold higher grades.
Nearby Lakes in Douglas County
Explore Diamond Lake across LakeGrade
More Oregon Lake Rankings
Other Grade F Lakes in Oregon
Eutrophic Lakes in Oregon
More records, surveys & data sources
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2025-09-24
Monitoring stations: 1