Polly Lake
Lake County, MinnesotaLimited DataEutrophic
Polly Lake earns a D — measurements through 2024 show persistent nutrient pressure that limits clarity through the summer.
Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. Polly Lake reaches 21 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. Polly Lake covers 485 acres alongside 18.6 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Within the 142 graded lakes of Lake County, Polly Lake sits at rank 127, near the bottom of the county list.
No invasive species are currently listed at Polly Lake — the lake remains off the Minnesota infested-waters roster. Walleye are documented at Polly Lake, one of 8 fish species on record for the lake. The lake lacks a documented public access point, so visitor use is limited. 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, Minnesota DNR LakeFinder, last sampled 2024-08-03. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Murky, only visible to about 4.5 ft. Trophic State Index: 55.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.5 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 55 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 21 ft |
| Average Depth | 9 ft |
| Surface Area | 485.24 acres |
| Shoreline Length | 18.6 mi |
| Littoral Zone | 78% |
| Public Access | No |
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for Polly Lake (14-day solunar calendar)
→ Is it safe to eat fish from Polly Lake? (mercury & PFAS guide)
→ Polly Lake fishing regulations (limits, seasons, special rules)
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.1 m/yr | 3 |
Location
County Ranking
Ranked #127 of 142 lakes in Lake County
Nearby Lakes in Lake County
More Minnesota Lake Rankings
Other Grade D Lakes in Minnesota
Eutrophic Lakes in Minnesota
Compare Polly Lake With Nearby Lakes
DNR Fisheries Survey Summary
3 surveys on file from MN DNR Fisheries. Most recent: 2016-09-12 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| White Sucker | 10.55 | 1.69 lb |
| Walleye | 7.58 | 0.88 lb |
| Yellow Perch | 3.12 | 0.15 lb |
| Green Sunfish | 1.71 | — |
| BNS | 1.29 | — |
| Pumpkinseed | 0.93 | 0.07 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
White Sucker
Walleye
Yellow Perch
Pumpkinseed
From the 2016-09-12 survey
Polly Lake has an area of 485 acres with a maximum depth of 21 feet and has brown tinted water with clarity around 7 feet. The lake is located within the BWCAW about 23 miles northeast of Isabella, and is a part of a popular canoe route called the Girl Chain. There are three portage routes into the lake. An 85 rod…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Polly Lake. 1 report on file.
- —Fisheries Lake Survey — PollyFisheries Lake Survey · MN DNR LakeFinder
EPA Impairment Status
Polly Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN38-0104-00 · 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
Lake details from Minnesota DNR LakeFinder
Most recent sample: 2024-08-03
Monitoring stations: 3