Washington County Lake Quality
Wisconsin, 3 lakes, average grade C (Fair)
Washington County has 3 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 average is C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.
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. Hadlock Pond (B) is the cleanest in the county.
Quick Answers for Washington County
Planning a trip? Check special fishing regulations for Hadlock Pond, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Washington County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Hadlock Pond | B | 14.6 ft | - | - |
| 2 | Cossayuna Lake | C | 8.8 ft | - | - |
| 3 | Southern Section Lake | D | 2 ft | - | 36.7 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.