Pepin Lake
Pepin County, WisconsinLimited DataHypereutrophic
Pepin Lake earns an F: phosphorus readings still being added and clarity at 1.5 ft signal heavy nutrient loading from the surrounding watershed. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.
The hypereutrophic status — TSI 71 — reflects sustained heavy nutrient loading from the surrounding watershed and frequent algal pressure. The lake's 60 ft maximum depth is in the upper tier for Wisconsin — deep enough for cold-water fish to find refuge in summer. Pepin Lake covers 24,550 acres alongside partial shoreline records, large enough that conditions can vary meaningfully between bays.
Zebra mussel presence at Pepin Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. The fishery is bass-led, with 3 documented species across the lake's records. Public access is available — the lake is on the Wisconsin DNR public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-06-05. Grade methodology: LakeGrade methodology.
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 1.5 ft of visibility. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.5 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 60 ft |
| Surface Area | 24,550 acres |
| Public Access | Yes |
Fish Species
Click a species to see every graded lake where it is documented.
→ Best fishing times for Pepin Lake (14-day solunar calendar)
→ Is it safe to eat fish from Pepin Lake? (mercury & PFAS guide)
→ Pepin Lake fishing regulations (limits, seasons, special rules)
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.06 m/yr | 2 |
Recreation & Access
Location
County Ranking
Ranked #1 of 1 lakes in Pepin County
Cleaner Lakes Within 30 Miles
Pepin Lake holds Grade F. 2 nearby lakes hold higher grades.
Nearby Lakes in Pepin County
More Wisconsin Lake Rankings
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Hypereutrophic Lakes in Wisconsin
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WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 6 stations on file (most recent sample 2015).
Fish Species (DNR-rated)
EPA Impairment Status
Pepin Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit WI10030300 · Official waterbody report
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Fish and recreation data from Wisconsin DNR Lakes
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2025-06-05
Monitoring stations: 1
Where to stay near Pepin Lake
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