Mercer County Lake Quality
Wisconsin, 2 lakes, average grade C (Fair)
Only 2 lakes in Mercer 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. 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 Lake Marie (B); the most-stressed is Lake Paho (D).
Quick Answers for Mercer County
Planning a trip? Check special fishing regulations for Lake Marie, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Mercer County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Lake Marie | B | 7.8 ft | - | 13 µg/L |
| 2 | Lake Paho | D | 2.2 ft | - | 37 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.