Jefferson County Lake Quality
Wisconsin, 2 lakes, average grade A (Excellent)
Jefferson County has 2 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's average grade is A — among the cleanest in New York. 1 lakes pull an A on their own, and almost none fall into the D or F brackets.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Millsite Lake (A) is the cleanest in the county.
Quick Answers for Jefferson County
Planning a trip? Check special fishing regulations for Millsite Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Jefferson County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Millsite Lake | A | 27.9 ft | - | - |
| 2 | Butterfield Lake | B | 11.3 ft | - | - |
Source: EPA National Aquatic Resource Surveys, 2026.