Alton Lake
Cook County, MinnesotaLimited DataOligotrophic
Alton Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season.
Trophically, Alton Lake reads as oligotrophic — nutrient-poor, clear, and ecologically more sensitive to disturbance than richer lakes. The lake's 72 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. Alton Lake covers 969 acres alongside 15.4 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Alton Lake ranks 57 of 128 in Cook County — solidly in the upper half of the local distribution.
No invasive species are currently listed at Alton Lake — the lake remains off the Minnesota infested-waters roster. Walleye are documented at Alton Lake, one of 7 fish species on record for the lake. No formal public access is documented at Alton Lake — most use is by shoreline residents and their guests. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-08-11. Grade methodology: LakeGrade methodology.
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B, Good
Good clarity, visible to about 13.5 ft. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13.5 ft | B |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 40 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 72 ft |
| Surface Area | 968.63 acres |
| Shoreline Length | 15.4 mi |
| Littoral Zone | 33% |
| Public Access | No |
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for Alton Lake (14-day solunar calendar)
→ Is it safe to eat fish from Alton Lake? (mercury & PFAS guide)
→ Alton Lake fishing regulations (limits, seasons, special rules)
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.535 m/yr | 2 |
Location
County Ranking
Ranked #57 of 128 lakes in Cook County
Nearby Lakes in Cook County
More Minnesota Lake Rankings
State Parks Near Alton Lake
Other Grade B Lakes in Minnesota
Oligotrophic Lakes in Minnesota
Compare Alton Lake With Nearby Lakes
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2025-08-04 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Tullibee (Cisco) | 18.70 | 0.99 lb |
| White Sucker | 5.82 | 2.43 lb |
| Walleye | 2.61 | 2.84 lb |
| Smallmouth Bass | 2.25 | 1.23 lb |
| Rock Bass | 1.80 | 0.27 lb |
| Northern Pike | 0.85 | 3.62 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.
Tullibee (Cisco)
White Sucker
Walleye
Smallmouth Bass
From the 2025-08-04 survey
Temperature and dissolved oxygen (DO) measurements were collected from the deepest basin in Alton Lake on August 4th, 2025, to evaluate the quantity and quality of cold, oxygenated water (i.e., oxythermal habitat) available to Cisco, also known as Tullibee, the most sensitive coldwater species present in this lake.…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Alton Lake. 1 report on file.
- —Fisheries Lake Survey — AltonFisheries Lake Survey · MN DNR LakeFinder
EPA Impairment Status
Alton Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN16-0622-00 · 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: 2024-08-11
Monitoring stations: 2