O'Brien Lake
| Iron | 76 |
O'Brien Springs
| Langlade | 0.36 |
O'Day Lake
| Oneida | 38 |
O'Leary Lake
| Grant | 7 |
O'Neil Creek Flowage # 2
| Chippewa | 70 |
O'Neil Creek Flowage Number One
| Chippewa | 32 |
Oak Creek Parkway Pond
| Milwaukee | 4 |
Oak Lake
| Washburn | 29 |
Oak Lake
| Burnett | 183 |
Oak Lake
| Lincoln | 8 |
Oak Lake
| Forest | 50 |
Oak Lake
| Iron | 30 |
Oak Lake
| Washburn | 93 |
Oak Ridge Lake
| St. Croix | 158 |
Oakwood Lake (U Merrillan Pond)
| Jackson | 15 |
Oatmeal Lake
| Oneida | 91 |
Obadash Lake
| Iron | 11 |
Oberlin Lake
| Vilas | 42 |
Obrien Springs, Lower
| Langlade | 1 |
Oconomowoc Lake
| Waukesha | 818 |