Randolph County Lake Quality
Wisconsin, 7 lakes, average grade D (Poor)
Randolph County has 7 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. The county-wide average grade is D — water quality issues are persistent across most of the monitored basins. 0 lakes fall into the F bracket outright.
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 Old Reservoir (C); the most-stressed is Sugar Creek Lake North Arm (D).
Quick Answers for Randolph County
Planning a trip? Check special fishing regulations for Old Reservoir, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Randolph County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Old Reservoir | C | 3.6 ft | - | 33 µg/L |
| 2 | Rothwell Lake | C | 3.6 ft | - | 32 µg/L |
| 3 | Sugar Creek Lake | D | 2.5 ft | - | 50.5 µg/L |
| 4 | Cedar Lake | D | 2.7 ft | - | 51.8 µg/L |
| 5 | Sugar Creek Lake | D | 2.5 ft | - | 45 µg/L |
| 6 | Thomas Hill Res. Nr. Dam Lake | D | 2.3 ft | - | 61 µg/L |
| 7 | Sugar Creek Lake North Arm | D | 1.6 ft | - | 71.3 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.