Johnson County Lake Quality
Wisconsin, 5 lakes, average grade C (Fair)
Johnson County has 5 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. The county average is C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.
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 Rock Lake Village Lake (B); the most-stressed is Holden City Lake Nr. Dam (F).
Quick Answers for Johnson County
Planning a trip? Check special fishing regulations for Rock Lake Village Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Johnson County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Rock Lake Village Lake | B | 4.3 ft | - | 16 µg/L |
| 2 | Lake Buteo | B | 5.6 ft | - | 20 µg/L |
| 3 | Knob Noster S.P. Lake 2 | C | 3.9 ft | - | 29 µg/L |
| 4 | Hazel Hill Lake by Dam | D | 2 ft | - | 59.3 µg/L |
| 5 | Holden City Lake Nr. Dam | F | 2 ft | - | 96 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.