Jefferson County Lake Quality
Wisconsin, 8 lakes, average grade C (Fair)
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. 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 Rock Lake (A); the most-stressed is Lake Koshkonong (F).
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 | 12.5 ft | 60 ft | 17.9 µg/L |
| 2 | Lake Ripley | B | 8.8 ft | 44 ft | 22.3 µg/L |
| 3 | Red Cedar Lake | C | 4.3 ft | 6 ft | 23.7 µg/L |
| 4 | Blue Spring Lake | C | 6 ft | 27 ft | 23.8 µg/L |
| 5 | Hope Lake | C | 8 ft | 24 ft | - |
| 6 | Lower Spring Lake | C | 5 ft | - | 46.9 µg/L |
| 7 | Mud Lake | D | 2.1 ft | 22 ft | 63.1 µg/L |
| 8 | Lake Koshkonong | F | 1.7 ft | 7 ft | 287 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.