Marathon County Lake Quality
Wisconsin, 5 lakes, average grade C (Fair)
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 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. Big Bass Lake (B) is the cleanest in the county.
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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.
Fishing in Marathon County
DNR Reports (5)
Wisconsin DNR Fisheries Survey resources for lakes in Marathon County. browse all reports →
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- 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
5 lakes · 4 graded, 1 not rated4 graded lakes · 1 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Max Depth | Access |
|---|---|---|---|---|---|---|---|---|
| 1 | BBig Bass LakeMarathon | B | 6 ft | 19 µg/L | No recent samples | No recent samples | 13 ft | ✓ Public |
| 2 | CPike LakeMarathon | C | 5 ft | 29.3 µg/L | No recent samples | No recent samples | 34 ft | ✓ Public |
| 3 | DBig Eau Pleine LakeMarathon | D | 1.5 ft | 131 µg/L | No recent samples | No recent samples | No recent samples | ✓ Public |
| 4 | DLake DubayMarathon | D | 2.5 ft | 64.9 µg/L | No recent samples | No recent samples | No recent samples | ✓ Public |
| NRBig Eau Pleine Southeast Point LakeMarathon | NR | 1.5 ft | No recent samples | No recent samples | No recent samples | 46 ft | ✓ Public |
NR = not rated: the monitoring record does not meet the evidence bar for a grade. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Other Counties in Wisconsin
See how Marathon County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 39 states and 2 Canadian provinces.
Source: EPA National Aquatic Resource Surveys, 2026.