Marathon County Lake Quality
Wisconsin, 5 lakes, average grade D (Poor)
Marathon County has 5 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. 2 lakes fall into the F bracket outright.
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. Big Bass Lake (B) is the cleanest in the county.
Quick Answers for Marathon County
Planning a trip? Check special fishing regulations for Big Bass Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
DNR Reports (5)
Wisconsin DNR Fisheries Survey resources for lakes in Marathon County. browse all reports →
- 2025Wisconsin River walleye recruitment survey, 2025Walleye Survey · WI DNR · 2025 (PDF)
- 2024Big Eau Pleine Reservoir comprehensive survey, 2024Comprehensive Survey · WI DNR · 2024 (PDF)
- —Lake DuBay comprehensive survey 2022Comprehensive Survey · WI DNR (PDF)
- —Pike Lake comprehensive survey 2021Comprehensive Survey · WI DNR (PDF)
- —Wadley Lake summer survey 2022Fisheries Survey · WI DNR (PDF)
All Lakes in Marathon County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Big Bass Lake | B | 6 ft | 13 ft | 19 µg/L |
| 2 | Pike Lake | C | 5 ft | 34 ft | 29.3 µg/L |
| 3 | Lake Dubay | D | 2.5 ft | - | 63.6 µg/L |
| 4 | Big Eau Pleine Lake | F | 1.5 ft | - | 131 µg/L |
| 5 | Big Eau Pleine Southeast Point Lake | F | 1.5 ft | 46 ft | - |
Source: EPA National Aquatic Resource Surveys, 2026.