Sully County Lake Quality
Wisconsin, 1 lakes, average grade B (Good)
Sully County has 1 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. With an average grade of B, Sully County sits comfortably above the South Dakota median.
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 Oahlk1110dw Lake (B); the most-stressed is Oahlk1110dw Lake (B).
Quick Answers for Sully County
Planning a trip? Check special fishing regulations for Oahlk1110dw Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Sully County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Oahlk1110dw Lake | B | 12.8 ft | - | 10 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.