Jefferson County Lake Quality
Wisconsin, 8 lakes, average grade B (Good)
Only 8 lakes in Jefferson County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. With an average grade of B, Jefferson County sits comfortably above the Wisconsin 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 Rock Lake (A); the most-stressed is Lake Koshkonong (D).
Quick Answers for Jefferson County
Planning a trip? Check special fishing regulations for Rock Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
DNR Reports (4)
Wisconsin DNR Fisheries Survey resources for lakes in Jefferson County. browse all reports →
- 2025Lower Spring Lake spring shocking survey, 2025Spring Shocking Survey · WI DNR · 2025 (PDF)
- 2023Lake Ripley comprehensive survey, 2023Comprehensive Survey · WI DNR · 2023 (PDF)
- 2023Lower Spring Lake Spring summary report, 2023Fisheries Survey · WI DNR · 2023 (PDF)
- 2022Rock Lake comprehensive survey, 2022Comprehensive Survey · WI DNR · 2022 (PDF)
All Lakes in Jefferson County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Rock Lake | A | 39.4 ft | 60 ft | 17.9 µg/L |
| 2 | Hope Lake | A | 26.2 ft | 24 ft | - |
| 3 | Lake Ripley | A | 27.9 ft | 44 ft | 22.3 µg/L |
| 4 | Blue Spring Lake | A | 19.7 ft | 27 ft | 23.8 µg/L |
| 5 | Lower Spring Lake | B | 16.4 ft | - | 46.9 µg/L |
| 6 | Red Cedar Lake | B | 13.1 ft | - | 23.7 µg/L |
| 7 | Mud Lake | C | 7.4 ft | 22 ft | 63.1 µg/L |
| 8 | Lake Koshkonong | D | 5.7 ft | 7 ft | 287 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.