Onagon Lake
Onagon Lake in Cook County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 6 ft visibility. Maximum depth: 15 ft. Surface area: 31.26 acres.
- Clarity
- 6 ft
- Max depth
- 15 ft
- Area
- 31 acres
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in Cook County
Why Onagon 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 Onagon Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. 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.
Onagon Lake is a 31-acre lake in Cook County, Minnesota with a maximum depth of 15 feet. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-03. Grade methodology: LakeGrade methodology.
Watch Onagon Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Onagon Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Murky, only visible to about 6 ft. Trophic State Index: 51.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Onagon Lake
Compare lakeside cabins, hotels, and vacation rentals near Onagon 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 Onagon Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 15 ft |
| Surface Area | 31 acres |
| Shoreline Length | 1.4 mi |
| Littoral Zone | 100% |
| Public Access | Yes |
Recreation & Access
- SaganagaPublic
- Sea Gull Lake (East)Public
Fishing Onagon Lake
DNR Fisheries Survey Summary
1 survey on file from MN DNR Fisheries. Most recent: 1972-09-01 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Yellow Perch | 13.33 | 0.35 lb |
| Northern Pike | 9.33 | 1.32 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
From the 1972-09-01 survey
Ambush Lk has a large N Pike population with a good distribution of sizes. A forage species. Yel Perch are abundant with a good proportion of angling size, 10-12 inches.
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Onagon Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — AmbushFisheries Lake Survey · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.098 m/yr | 6 |
| Phosphorus | ↓ Declining | +0.2 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +0.35 µg/L/yr | 5 |
EPA Impairment Status
Onagon 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 MN16-0632-01 · Official waterbody report · Matched by proximity (1.81 km)
Graded lakes near Onagon Lake
Onagon Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Cook County
Frequently asked questions about Onagon Lake
What is the water quality grade for Onagon Lake?
- Onagon Lake in Cook County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 6 ft visibility. Maximum depth: 15 ft. Surface area: 31.26 acres.
Is Onagon Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Onagon 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 Onagon Lake?
- Onagon Lake has a maximum depth of 15 feet. The lake covers 31.26 acres.
Are there boat ramps on Onagon Lake?
- Onagon Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Saganaga, Sea Gull Lake (East). Public access is listed as yes.
Explore Onagon Lake across LakeGrade
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Cook County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Lake Superior Basin (MN+WI), ranked by water quality
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
Other Lakes in Minnesota
Eutrophic Lakes in Minnesota
Where this data comes from
26 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA26 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (1)
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 details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory