Cass Lake
Beltrami County, Minnesota15,958 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Cass Lake. Here is what has been measured.
- Oligotrophic
- zebra mussel
- 120 ft max depth
- Public access
- Limited data
Cass Lake in Beltrami County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 18.5 ft visibility. Phosphorus: 11 µg/L. Chlorophyll-a (algae): 3.2 µg/L. Maximum depth: 120 ft. Surface area: 15958.25 acres.
Minnesota DNR's Standard Survey on September 18, 2025 caught 7.80 walleye per gill net at Cass Lake. Length samples in the latest survey that recorded them ran 8–28 inches. DNR survey details →
Free interactive depth-contour map of Cass Lake, reaching a maximum surveyed depth of 120 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Cass Lake is a 15,958-acre cold, clear oligotrophic lake in Beltrami County, Minnesota with a maximum depth of 120 feet. The lake supports 21 documented fish species including black bullhead, black crappie, and bluegill. Public access is available. Compared to the 84 other monitored lakes in Beltrami County, Cass Lake ranks #59 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-15. Methodology: how these readings are compared.
At about 16,000 acres, Cass Lake is large enough that where you stay decides which shore you see most of. The median ice-out date is April 24, which is when the open-water season begins. Vrbo is where to look for cabins and lake homes around Cass Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Cass Lake is good for
From access and monitoring records, not editorial picks.
- Clear water18.5 ft of visibility
- Fishing21 species recorded
- Ice seasonIce-out around Apr 24
- Deep water120 ft surveyed max depth
- Big water15,958 acres
Swimming conditions
Readings onlyLimited data
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 Cass 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 Cass Lake
These are the measurements Minnesota PCA publishes for Cass 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 18.5 ft down. Phosphorus 11 µg/L. Chlorophyll-a 3.2 µg/L. TSI 39.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 18.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 11µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 3.2µg/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. | 39 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Cass Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Cass Lake typically sits around 54°F at the surface in October. Summer average is about 57°F. Usually warmest in Jul (about 60°F) and coldest in May (about 48°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (48°F) to its warmest (60°F).
Typical surface water temperature by month, from 293 field readings (2024–2025) via the EPA Water Quality Portal. See the full Cass Lake water temperature breakdown →
Minnesota DNR's Standard Survey on September 18, 2025 caught 7.80 walleye per gill net at Cass Lake. Length samples in the latest survey that recorded them ran 8–28 inches.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Cass Lake’s water-quality measurements separately. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
38 surveys on file from MN DNR Fisheries. Most recent: 2025-09-18 (Standard Survey).
38 surveys on file · most recent 2025-09-18 (Standard Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Yellow Perch | 234.53 | 5–12 in 2025-09-18 | 0.18 lb |
| Walleye | 21.07 | 8–28 in 2025-09-18 | 0.95 lb |
| Bluntnose Minnow | 13.08 |
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.
Yellow Perch
Walleye
From the 2025-09-18 survey
Cass Lake is a nearly 16,000 acre lake and is the largest lake in the Cass Lake chain, which altogether includes over 25,000 acres of connected waters. The lake has a mix of expansive, shallow flats and deeper water with lots of underwater structure. Walleye, Yellow Perch, and Muskellunge are the most sought-after…
Lake Details
Max depth
120 ft
Surface area
15,958 acres
Shoreline
45.4 mi
Littoral zone
20%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Stays via Stay22
Stays near Cass Lake
Compare lakeside cabins, hotels, and vacation rentals near Cass Lake in Beltrami 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 Cass Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
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Fish Species
Click a species to see every lake where it is documented.
Fishing Cass 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.
Ice season
Typical ice-out
Apr 24
Earliest Apr 6, 2021 · Latest May 12, 2008
Typical ice-in
Dec 4
Earliest Nov 24, 2008 · Latest Jan 7, 2024
Most recent ice-out
Apr 27
2025
16 observations · Minnesota PCA ice records
Nearby Lakes in Beltrami County
Frequently asked questions about Cass Lake
Where is Cass Lake?
- Cass Lake is a lake in Beltrami County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Cass Lake?
- Cass Lake in Beltrami County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 18.5 ft visibility. Phosphorus: 11 µg/L. Chlorophyll-a (algae): 3.2 µg/L. Maximum depth: 120 ft. Surface area: 15958.25 acres.
Is Cass Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Cass Lake?
- Cass Lake typically sits around 54°F at the surface in October, from 293 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Cass Lake?
- Cass Lake has a maximum depth of 120 feet. The lake covers 15958.25 acres.
What fish are in Cass Lake?
- Fish species found in Cass Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, burbot, greater redhorse, hybrid sunfish, lake whitefish, largemouth bass, muskellunge, northern pike, pumpkinseed, redhorse, rock bass, shorthead redhorse, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Cass Lake is located in Beltrami County, Minnesota.
What did the DNR fisheries survey find at Cass Lake?
- Minnesota DNR's Standard Survey on September 18, 2025 caught 7.80 walleye per gill net at Cass Lake. Length samples in the latest survey that recorded them ran 8–28 inches. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Cass Lake’s water-quality measurements separately. Catch rate is not a swim clearance and is not a weekly bite report.
When does Cass Lake thaw?
- Cass Lake typically has ice-out around Apr 24. Ice typically forms around Dec 4. The open water season is approximately 224 days.
Can I fish at Cass Lake?
- Public access to Cass Lake is listed as yes on the lake record. 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 Cass Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Fish species and the cleanest lakes across Minnesota
Fish species and best lakes in Beltrami County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its readings
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Minnesota's cleanest lakes, ranked on agency measurements
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Where this data comes from
23 measurements from 1 monitoring station, 2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Leech Lake Band of Ojibwe
LEECHLAK_WQX23 samples · 2025
Analytical methods
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Nitrate-Nitrite Nitrogen by Colorimetry
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 details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate