Alton Lake
Alton Lake in Cook County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13.5 ft visibility. Maximum depth: 72 ft. Surface area: 968.63 acres.
- Clarity
- 13.5 ft
- Max depth
- 72 ft
- Area
- 969 acres
- Trend
- ↓ Declining
- Public access
- No
Next lake in Cook County
Free interactive depth-contour map of Alton Lake, reaching a maximum surveyed depth of 70 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Why Alton Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Alton Lake, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Alton Lake is a 969-acre lake in Cook County, Minnesota with a maximum depth of 72 feet. Overall water quality is declining over recent sampling years. The lake supports 7 documented fish species including northern pike, rock bass, and smallmouth bass. No public access — the lake is private or restricted.
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
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Alton Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Good clarity, visible to about 13.5 ft. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13.5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Alton Lake
Compare lakeside cabins, hotels, and vacation rentals near Alton Lake in Cook County, Minnesota — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Alton Lake
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Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 72 ft |
| Surface Area | 969 acres |
| Shoreline Length | 15.4 mi |
| Littoral Zone | 33% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Alton Lake
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.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — AltonFisheries Lake Survey · MN DNR LakeFinder
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 |
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
Nearby Lakes in Cook County
Frequently asked questions about Alton Lake
What is the water quality grade for Alton Lake?
- Alton Lake in Cook County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13.5 ft visibility. Maximum depth: 72 ft. Surface area: 968.63 acres.
Is Alton Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Alton Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
How deep is Alton Lake?
- Alton Lake has a maximum depth of 72 feet. The lake covers 968.63 acres.
What fish are in Alton Lake?
- Fish species found in Alton Lake include northern pike, rock bass, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow perch. Alton Lake is located in Cook County, Minnesota.
Explore Alton Lake across LakeGrade
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Where this data comes from
2 measurements from 2 monitoring stations, 2022–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA2 samples · 2022–2024
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (2)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder