Mary Lake
Crow Wing County, Minnesota413 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Mary Lake. Here is what has been measured.
- Eutrophic
- Eurasian watermilfoil
- 34 ft max depth
Mary Lake in Crow Wing County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.9 ft visibility. Phosphorus: 20.5 µg/L. Chlorophyll-a (algae): 8.8 µg/L. Maximum depth: 34 ft. Surface area: 412.64 acres.
Minnesota DNR's Targeted Survey on July 1, 2024 caught 0.50 walleye per trap net at Mary Lake. DNR survey details →
Mary Lake is a 413-acre productive, nutrient-rich eutrophic lake in Crow Wing County, Minnesota with a maximum depth of 34 feet. Overall water quality is declining over recent sampling years. The lake supports 13 documented fish species including black bullhead, black crappie, and bluegill. No public access — the lake is private or restricted. Compared to the 84 other monitored lakes in Crow Wing County, Mary Lake ranks #72 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-14. Methodology: how these readings are compared.
What Mary Lake is good for
From access and monitoring records, not editorial picks.
- Fishing13 species recorded
- Ice seasonIce-out around Apr 15
- Deep water34 ft surveyed max depth
Swimming conditions
Readings onlyModerate 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 Mary 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 Mary Lake
These are the measurements Minnesota PCA publishes for Mary Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 4.9 ft. Phosphorus 20.5 µg/L. Chlorophyll-a 8.8 µg/L. TSI 51.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.9ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 20.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 8.8µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 51 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Mary Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Mary Lake typically sits around 69°F at the surface in September. Summer average is about 75°F. Usually warmest in Jul (about 78°F) and coldest in May (about 62°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (62°F) to its warmest (78°F).
Typical surface water temperature by month, from 25 field readings (2021–2025) via the EPA Water Quality Portal. See the full Mary Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Mary Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (25,823 cells/mL) on December 6, 2025.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Minnesota DNR's Targeted Survey on July 1, 2024 caught 0.50 walleye per trap net at Mary Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Mary 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: 2024-07-01 (Targeted Survey).
7 surveys on file · most recent 2024-07-01 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 16.76 | 2–8 in 2024-07-01 | 0.22 lb |
| Black Crappie | 5.43 | 3–9 in 2024-07-01 | 0.21 lb |
| Yellow Perch | 4.81 | 6–7 in 2024-07-01 | 0.14 lb |
| Fathead Minnow | 1.89 |
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.
Bluegill
Black Crappie
Yellow Perch
From the 2024-07-01 survey
A targeted survey of nearshore fish species in Mary Lake was conducted beginning on July 1, 2024, by Index of Biological Integrity (IBI) Program staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible.…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Mary Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — MaryFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — MaryFish Stocking History · MN DNR LakeFinder
Lake Details
Max depth
34 ft
Surface area
413 acres
Shoreline
4.7 mi
Littoral zone
31%
Share shallower than 15 ft
Public access
No
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
18 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,243 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Mary Lake
Compare lakeside cabins, hotels, and vacation rentals near Mary Lake in Crow Wing 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 Mary Lake
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Fish Species
Click a species to see every lake where it is documented.
Fishing Mary 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.
Water Quality Trend: Worsening
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening6 years
Phosphorus
Stable+0.41 µg/L/yr6 years
Chlorophyll-a
Worsening+0.2 µg/L/yr6 years
Ice season
Typical ice-out
Apr 15
Earliest Mar 18, 2016 · Latest May 2, 2023
Typical ice-in
Dec 10
Earliest Nov 14, 2002 · Latest Dec 17, 2015
Most recent ice-out
May 2
2023
12 observations · Minnesota PCA ice records
Nearby Lakes in Crow Wing County
Frequently asked questions about Mary Lake
Where is Mary Lake?
- Mary Lake is a lake in Crow Wing County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Mary Lake?
- Mary Lake in Crow Wing County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.9 ft visibility. Phosphorus: 20.5 µg/L. Chlorophyll-a (algae): 8.8 µg/L. Maximum depth: 34 ft. Surface area: 412.64 acres.
Is Mary 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 Mary Lake?
- Mary Lake typically sits around 69°F at the surface in September, from 25 EPA Water Quality Portal field readings (2021–2025). That is a typical value for the month, not a live reading.
How deep is Mary Lake?
- Mary Lake has a maximum depth of 34 feet. The lake covers 412.64 acres.
What fish are in Mary Lake?
- Fish species found in Mary Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, largemouth bass, northern pike, pumpkinseed, rock bass, walleye, white sucker, yellow bullhead, yellow perch. Mary Lake is located in Crow Wing County, Minnesota.
What did the DNR fisheries survey find at Mary Lake?
- Minnesota DNR's Targeted Survey on July 1, 2024 caught 0.50 walleye per trap net at Mary Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Mary 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 Mary Lake thaw?
- Mary Lake typically has ice-out around Apr 15. Ice typically forms around Dec 10. The open water season is approximately 239 days.
Does Mary Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Mary Lake (clouds, ice, or an off-season gap). The most recent reading was moderate (25,823 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Can I fish at Mary Lake?
- Public access to Mary 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 Mary Lake across LakeQuality
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Where to stay at Minnesota's top lakes, each with its readings
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Where this data comes from
90 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
MNPCA90 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
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