Ozaukee County Lake Quality
Wisconsin, 9 lakes, average grade C (Fair)
Ozaukee County has 9 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. Ozaukee 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 Unnamed Lake (A); the most-stressed is Thiensville Millpond (F).
Quick Answers for Ozaukee County
Planning a trip? Check special fishing regulations for Unnamed Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Ozaukee County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Unnamed Lake | A | - | - | 12.2 µg/L |
| 2 | Moldenhauer Lake | A | - | 32 ft | 12.2 µg/L |
| 3 | Sandhill Lake | B | 24.6 ft | - | 31.1 µg/L |
| 4 | Watts Lake | B | 23 ft | 31 ft | 43.1 µg/L |
| 5 | Cty E Pond | B | 12.3 ft | - | 33.6 µg/L |
| 6 | Spring Lake | C | 8 ft | 22 ft | - |
| 7 | Hawthorne Hills Pond | C | - | - | 57.6 µg/L |
| 8 | Thiensville Millpond | F | - | - | 166 µg/L |
| 9 | Grafton Millpond | F | - | - | 110 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.