Duncan Lake
Cook County, Minnesota477 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Duncan Lake. Here is what has been measured.
- Impaired · Mercury
- 130 ft max depth
- Limited data
Duncan Lake in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 21.5 ft visibility. Maximum depth: 130 ft. Surface area: 476.95 acres.
Minnesota DNR's Standard Survey on September 10, 2018 caught 0.33 smallmouth bass per gill net at Duncan Lake. DNR survey details →
Duncan Lake is a 477-acre lake in Cook County, Minnesota with a maximum depth of 130 feet (47-foot average). Overall water quality is declining over recent sampling years. The lake supports 5 documented fish species including cisco species, green sunfish, and lake trout. No public access — the lake is private or restricted.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-08-07. Methodology: how these readings are compared.
Duncan Lake covers about 480 acres in Cook County. Vrbo is where to look for cabins and lake homes around Duncan Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Duncan Lake is good for
From access and monitoring records, not editorial picks.
- Clear water21.5 ft of visibility
- Fishing5 species recorded
- Deep water130 ft surveyed max depth
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Duncan Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
Whether Duncan Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Duncan Lake
These are the measurements Minnesota PCA publishes for Duncan Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 21.5 ft down. TSI 33.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 21.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 33 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Duncan Lake
Answers come straight from the public measurements and survey records on this page.
Minnesota DNR's Standard Survey on September 10, 2018 caught 0.33 smallmouth bass per gill net at Duncan Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Duncan Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
7 surveys on file from MN DNR Fisheries. Most recent: 2025-08-11 (Targeted Survey).
7 surveys on file · most recent 2025-08-11 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Tullibee (Cisco) | 12.04 | 8–17 in 2001-08-06 | 0.74 lb |
| Green Sunfish | 3.40 | 5 in 2018-09-10 | 0.11 lb |
| White Sucker | 3.33 | 14–21 in 2018-09-10 | 2.41 lb |
| Yellow Perch | 3.25 | 5–10 in 2013-08-12 | 0.31 lb |
| Lake Trout | 2.05 | 9–35 in 2018-09-10 | 2.52 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
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)
Green Sunfish
White Sucker
Yellow Perch
From the 2025-08-11 survey
Temperature and dissolved oxygen (DO) measurements were collected from the deepest basin in Duncan Lake on August 11th, 2025, 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, also known…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Duncan Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — DuncanFisheries Lake Survey · MN DNR LakeFinder
Lake Details
Max depth
130 ft
Average depth
46.8 ft
Surface area
477 acres
Shoreline
7.6 mi
Littoral zone
31%
Share shallower than 15 ft
Public access
No
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
4 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,654 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Duncan Lake
Compare lakeside cabins, hotels, and vacation rentals near Duncan 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 Duncan Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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Fish Species
Click a species to see every lake where it is documented.
Fishing Duncan Lake
Water Quality Trend: Worsening
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening6 years
Phosphorus
Worsening+0.5 µg/L/yr4 years
Chlorophyll-a
Worsening+0.08 µg/L/yr4 years
EPA Impairment Status
Duncan Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Fish consumption.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN16-0232-00 · Official waterbody report
Nearby Lakes in Cook County
Frequently asked questions about Duncan Lake
Where is Duncan Lake?
- Duncan Lake is a lake in Cook County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Duncan Lake?
- Duncan Lake in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 21.5 ft visibility. Maximum depth: 130 ft. Surface area: 476.95 acres.
Is Duncan Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Duncan Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
How deep is Duncan Lake?
- Duncan Lake has a maximum depth of 130 feet and an average depth of 46.8 feet. The lake covers 476.95 acres.
What fish are in Duncan Lake?
- Fish species found in Duncan Lake include cisco species, green sunfish, lake trout, smallmouth bass, white sucker. Duncan Lake is located in Cook County, Minnesota.
What did the DNR fisheries survey find at Duncan Lake?
- Minnesota DNR's Standard Survey on September 10, 2018 caught 0.33 smallmouth bass per gill net at Duncan Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Duncan Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Can I fish at Duncan Lake?
- Public access to Duncan Lake is listed as no on the lake record, so confirm before you make the trip. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
Explore Duncan Lake across LakeQuality
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Where this data comes from
5 measurements from 5 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
MNPCA5 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (5)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from 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