Cooper Lake
Cass County, Minnesota133 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Cooper Lake. Here is what has been measured.
- Oligotrophic
- 70 ft max depth
Cooper Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 17.1 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 3.1 µg/L. Maximum depth: 70 ft. Surface area: 132.53 acres.
Minnesota DNR's Standard Survey on July 6, 1987 caught 0.33 walleye per gill net at Cooper Lake. DNR survey details →
Cooper Lake is a 133-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 70 feet. Overall water quality is declining over recent sampling years. The lake supports 12 documented fish species including black crappie, bluegill, and bowfin (dogfish). No public access — the lake is private or restricted. Compared to the 103 other monitored lakes in Cass County, Cooper Lake ranks #62 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-29. Methodology: how these readings are compared.
Cooper Lake covers about 130 acres in Cass County. The median ice-out date is April 17, which is when the open-water season begins. If you are planning to stay, you can search lake houses and cabins around Cooper Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Cooper Lake is good for
From access and monitoring records, not editorial picks.
- Clear water17.1 ft of visibility
- Fishing12 species recorded
- Ice seasonIce-out around Apr 17
- Deep water70 ft surveyed max depth
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Cooper 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 Cooper Lake
These are the measurements Minnesota PCA publishes for Cooper 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 17.1 ft down. Phosphorus 13 µg/L. Chlorophyll-a 3.1 µg/L. TSI 40.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 17.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 13µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 3.1µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 40 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Cooper Lake
Answers come straight from the public measurements and survey records on this page.
Minnesota DNR's Standard Survey on July 6, 1987 caught 0.33 walleye per gill net at Cooper Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Cooper 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
2 surveys on file from MN DNR Fisheries. Most recent: 1987-07-06 (Standard Survey).
2 surveys on file · most recent 1987-07-06 (Standard Survey)
39 years old| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 41.02 | 0.12 lb | |
| Pumpkinseed | 18.97 | 0.15 lb | |
| Tullibee (Cisco) | 17.34 | 0.57 lb | |
| Yellow Perch | 4.89 | 0.13 lb | |
| Rock Bass | 4.17 | 0.24 lb | |
| Northern Pike | 2.64 | 3.45 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.
From the 1987-07-06 survey
ALTHOUGH BLACK CRAPPIE WERE NOT TAKEN DURING THE SURVEY, THE OWNER OF CAMP SECLUSION SAID IT WAS AN EXCELLENT WINTER AND SUMMER CRAPPIE FISHING LAKE. ANY WALLEYE THAT ARE CAUGHT ARE LARGE.THE FISH POPULATION LOOKS VERY SIMILAR TO WHAT WAS FOUND IN THE 1973 SURVEY WITH THE BULK OF THE POPULATION MADE UP OF CENTRARCHIDS…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Cooper Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — CooperFisheries Lake Survey · MN DNR LakeFinder
Lake Details
Max depth
70 ft
Surface area
133 acres
Shoreline
3 mi
Littoral zone
73%
Share shallower than 15 ft
Public access
No
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
1 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,309 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Cooper Lake
Compare lakeside cabins, hotels, and vacation rentals near Cooper Lake in Cass 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 Cooper Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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 →
Follow Cooper Lake’s readings
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Fish Species
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Fishing Cooper Lake
Water Quality Trend: Worsening
Based on 6 years of monitoring (2020–2025).
Water clarity
Stable6 years
Phosphorus
Worsening+1.37 µg/L/yr6 years
Chlorophyll-a
Stable-0.06 µg/L/yr6 years
Ice season
Typical ice-out
Apr 17
Earliest Apr 14, 2005 · Latest Apr 30, 2008
Typical ice-in
Dec 2
Earliest Nov 25, 2003 · Latest Dec 4, 2004
Most recent ice-out
Apr 30
2008
8 observations · Minnesota PCA ice records
Nearby Lakes in Cass County
Frequently asked questions about Cooper Lake
Where is Cooper Lake?
- Cooper Lake is a lake in Cass County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Cooper Lake?
- Cooper Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 17.1 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 3.1 µg/L. Maximum depth: 70 ft. Surface area: 132.53 acres.
Is Cooper Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is Cooper Lake?
- Cooper Lake has a maximum depth of 70 feet. The lake covers 132.53 acres.
What fish are in Cooper Lake?
- Fish species found in Cooper Lake include black crappie, bluegill, bowfin (dogfish), greater redhorse, hybrid sunfish, largemouth bass, northern pike, northern pike (silver phase), pumpkinseed, rock bass, yellow bullhead, yellow perch. Cooper Lake is located in Cass County, Minnesota.
What did the DNR fisheries survey find at Cooper Lake?
- Minnesota DNR's Standard Survey on July 6, 1987 caught 0.33 walleye per gill net at Cooper Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Cooper 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.
When does Cooper Lake thaw?
- Cooper Lake typically has ice-out around Apr 17. Ice typically forms around Dec 2. The open water season is approximately 229 days.
Can I fish at Cooper Lake?
- Public access to Cooper 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.
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Where this data comes from
42 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
MNPCA42 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 (1)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate