Jefferson County Lake Quality

Jefferson County's 22 monitored lakes fall in the moderate-density bracket for Oregon. 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. 6 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. On average, Jefferson County lakes grade D, with phosphorus loading and reduced clarity showing up across most of the dataset.

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 (C); the most-stressed is Deschutes River Arm Lake (D).