Otsego County Lake Quality
Wisconsin, 13 lakes, average grade A (Excellent)
Only 13 lakes in Otsego 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's average grade is A — among the cleanest in Michigan. 11 lakes pull an A on their own, and almost none fall into the D or F brackets.
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 Opal Lake Central Basin;Otesgo Lake Township Sec12 (A); the most-stressed is Viking Lake Central Basin; Otsego Lake Township; T29n R3w Sect 24 (C).
Quick Answers for Otsego County
Planning a trip? Check special fishing regulations for Opal Lake Central Basin;Otesgo Lake Township Sec12, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Otsego County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Opal Lake Central Basin;Otesgo Lake Township Sec12 | A | 18.5 ft | - | - |
| 2 | Town Line Lake Northeast Basin; Chester Township | A | 16.5 ft | - | - |
| 3 | Town Line Lake | A | 16.5 ft | - | - |
| 4 | Opal Lake | A | 18.5 ft | - | - |
| 5 | Big Bear Lake East Basin; Charlton Township T29n R1w. Section 1 | A | 15 ft | - | - |
| 6 | O'Rourke Lake | A | 15.5 ft | - | - |
| 7 | O'Rourke Lake; Bagley Twp | A | 15 ft | - | - |
| 8 | Big Bear Lake | A | 15 ft | - | - |
| 9 | Douglas Lake | A | 16.5 ft | - | - |
| 10 | Kassuba Lake; Bagley Township; Section 12 | A | 20.5 ft | - | - |
| 11 | Perch Lake | A | 11.3 ft | - | - |
| 12 | Perch Lakes | B | 10.5 ft | - | - |
| 13 | Viking Lake Central Basin; Otsego Lake Township; T29n R3w Sect 24 | C | 2.5 ft | - | - |
Source: EPA National Aquatic Resource Surveys, 2026.