Jefferson County Lake Quality
Oregon, 15 lakes, average grade C (Fair)
Jefferson County's 15 graded lakes fall in the moderate-density bracket for {{stateName}}. The county-level average smooths over real differences — a single agricultural watershed near the southwest corner can pull the average down even if the rest of the county runs clean. Jefferson County averages to a C. The distribution behind that average matters more than the letter: a few stressed lakes versus many decent ones can produce the same average as the inverse.
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 Billy Chinook Reservoir (B); the most-stressed is Lake Billy Chinook (F).
Quick Answers for Jefferson County
Planning a trip? Check special fishing regulations for Billy Chinook Reservoir — or check the official Oregon fishing regulations.
All Lakes in Jefferson County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Billy Chinook Reservoir | B | 8.4 ft | - |
| 2 | Lake Billy Chinook Metolius Arm | B | - | - |
| 3 | Deschutes River Arm Lake | B | 4.6 ft | - |
| 4 | Billy Chinook Reservoir | B | 4.4 ft | - |
| 5 | Lake Billy Chinook | D | - | - |
| 6 | Crooked River Arm Lake | D | - | - |
| 7 | Lake Billy Chinook | F | - | - |
| 8 | Deschutes River Arm Lake | F | - | - |
| 9 | Lake Billy Chinook | F | - | - |
| 10 | Lake Billy Chinook | F | - | - |
Other Counties in Oregon
See how Jefferson County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 27 states.
Where to stay near Jefferson County
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Source: EPA National Aquatic Resource Surveys, 2026.