Gunflint Lake
Gunflint Lake in Cook County, Minnesota has a water quality grade of A (Excellent). Water clarity: 16.5 ft visibility. Phosphorus: 5.5 µg/L. Chlorophyll-a (algae): 2.6 µg/L. Maximum depth: 200 ft. Surface area: 4009.12 acres.
- Clarity
- 16.5 ft
- Typical in August
- 55°F
- Max depth
- 200 ft
- Area
- 4,009 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- May 6
- Open water
- 217 days
Next lake in Cook County
Gunflint Lake is a 4,009-acre cold, clear oligotrophic lake in Cook County, Minnesota with a maximum depth of 200 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 12 documented fish species including bluegill, burbot, and cisco species. Public access is available with 2 public boat landings. Compared to the 43 other monitored lakes in Cook County, Gunflint Lake ranks #20 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-23. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Crystal clear, you can see 16.5 ft down. Phosphorus level: 5.5 µg/L. Chlorophyll-a: 2.6 µg/L. Trophic State Index: 35.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 16.5 ft | Not graded |
| Phosphorus | 5.5 µg/L | Good |
| Chlorophyll-a (Algae) | 2.6 µg/L | Good |
| Trophic State Index (TSI) | 35 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Gunflint Lake
Compare lakeside cabins, hotels, and vacation rentals near Gunflint 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.
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Water Temperature
Gunflint Lake typically sits around 55°F at the surface in August. Summer average is about 56°F. Usually warmest in Sep (about 58°F) and coldest in May (about 45°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 181 field readings (2024–2025) via the EPA Water Quality Portal. See the full Gunflint Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 200 ft |
| Surface Area | 4,009 acres |
| Shoreline Length | 39.2 mi |
| Littoral Zone | 17% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Loon LakePublic
- Gunflint LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Gunflint Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
DNR Fisheries Survey Summary
13 surveys on file from MN DNR Fisheries. Most recent: 2025-08-11 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| RBS | 6.77 | 0.02 lb |
| Rock Bass | 4.78 | 0.32 lb |
| Walleye | 3.96 | 1.4 lb |
| Tullibee (Cisco) | 3.42 | 0.22 lb |
| CIS | 3.32 | 0.24 lb |
| White Sucker | 2.03 | 2.29 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.
RBS
Rock Bass
Walleye
Tullibee (Cisco)
From the 2025-08-11 survey
Temperature and dissolved oxygen measurements were collected from the deepest basin in Gunflint Lake on August 11th, 2025. This was done to evaluate the quantity and quality of cold, oxygenated water (i.e., oxythermal habitat) available to Lake Trout, the most sensitive coldwater species present in this lake (Cisco,…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Gunflint Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — GunflintFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Gunflint (1800)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — GunflintFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — GunflintPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.314 m/yr | 5 |
Ice Season
Historical ice data from Minnesota DNR (87 observations).
Estimated open water season: 217 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-23 (2012) | 1936-06-03 (1936) |
| Ice-In | 2002-11-27 (2002) | 2001-12-23 (2001) |
Most recent ice-out: 2023-05-12
EPA Impairment Status
Gunflint 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 MN16-0356-00 · Official waterbody report
County Ranking
Ranked #20 of 44 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Gunflint Lake
What is the water quality grade for Gunflint Lake?
- Gunflint Lake in Cook County, Minnesota has a water quality grade of A (Excellent). Water clarity: 16.5 ft visibility. Phosphorus: 5.5 µg/L. Chlorophyll-a (algae): 2.6 µg/L. Maximum depth: 200 ft. Surface area: 4009.12 acres.
Is Gunflint Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Gunflint Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Gunflint Lake?
- Gunflint Lake typically sits around 55°F at the surface in August, from 181 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Gunflint Lake?
- Gunflint Lake has a maximum depth of 200 feet. The lake covers 4009.12 acres.
What fish are in Gunflint Lake?
- Fish species found in Gunflint Lake include bluegill, burbot, cisco species, lake trout, northern pike, rainbow smelt, rock bass, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow perch. Gunflint Lake is located in Cook County, Minnesota.
When does Gunflint Lake thaw?
- Gunflint Lake typically has ice-out around May 6. Ice typically forms around Dec 9. The open water season is approximately 217 days.
Are there boat ramps on Gunflint Lake?
- Gunflint Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Loon Lake, Gunflint Lake. Public access is listed as yes.
Explore Gunflint Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Species activity outlook by water temperature and season
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Where this data comes from
32 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA32 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate