Mary Lake
Mary Lake in Wright County, Minnesota has a water quality grade of C (Fair). Water clarity: 8.9 ft visibility. Phosphorus: 21 µg/L. Chlorophyll-a (algae): 8.3 µg/L. Maximum depth: 46 ft. Surface area: 189.97 acres.
- Clarity
- 8.9 ft
- Typical in August
- 63°F
- Max depth
- 46 ft
- Area
- 190 acres
- Type
- Mesotrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 9
- Open water
- 236 days
Next lake in Wright County
Mary Lake is a 190-acre mesotrophic lake in Wright County, Minnesota with a maximum depth of 46 feet (18-foot average). Water quality is graded C based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 13 documented fish species including black crappie, bluegill, and brown bullhead. Public access is available with 1 public boat landing. Compared to the 50 other monitored lakes in Wright County, Mary Lake ranks #19 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-17. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Moderate clarity, visible to about 8.9 ft. Phosphorus level: 21 µg/L. Chlorophyll-a: 8.3 µg/L. Trophic State Index: 48.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.9 ft | Not graded |
| Phosphorus | 21 µg/L | Good |
| Chlorophyll-a (Algae) | 8.3 µg/L | Fair |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Mary Lake
Compare lakeside cabins, hotels, and vacation rentals near Mary Lake in Wright 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
Mary Lake typically sits around 63°F at the surface in August. Summer average is about 62°F. Usually warmest in Sep (about 64°F) and coldest in May (about 53°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 145 field readings (2011–2023) via the EPA Water Quality Portal. See the full Mary Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 46 ft |
| Average Depth | 17.8 ft |
| Surface Area | 190 acres |
| Shoreline Length | 2.3 mi |
| Littoral Zone | 45% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Johnson ParkPublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Mary Lake
DNR Fisheries Survey Summary
9 surveys on file from MN DNR Fisheries. Most recent: 2024-07-22 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 47.53 | 0.15 lb |
| Green Sunfish | 12.36 | 0.11 lb |
| Yellow Bass | 10.19 | 0.84 lb |
| Largemouth Bass | 9.92 | 0.68 lb |
| Yellow Perch | 7.07 | 0.12 lb |
| UK2 | 6.12 | — |
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.
Bluegill
Green Sunfish
Yellow Bass
Largemouth Bass
From the 2024-07-22 survey
A targeted survey of nearshore fish species in Mary Lake was conducted beginning on July 22nd, 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
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.895 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.51 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.41 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (170 observations).
Estimated open water season: 236 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 1990-03-03 (1990) | 2018-05-02 (2018) |
| Ice-In | 1991-11-15 (1991) | 2001-12-20 (2001) |
Most recent ice-out: 2023-04-19
EPA Impairment Status
Mary 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 MN86-0193-00 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Mary Lake under Clean Water Act (NPDES) discharge permits.
- Tioga Dairy LlcWaverly · 3.6 mi away · NPDES MN0064041
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #19 of 51 lakes in Wright County
Nearby Lakes in Wright County
Frequently asked questions about Mary Lake
What is the water quality grade for Mary Lake?
- Mary Lake in Wright County, Minnesota has a water quality grade of C (Fair). Water clarity: 8.9 ft visibility. Phosphorus: 21 µg/L. Chlorophyll-a (algae): 8.3 µg/L. Maximum depth: 46 ft. Surface area: 189.97 acres.
Is Mary Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Mary Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 8.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Mary Lake?
- Mary Lake typically sits around 63°F at the surface in August, from 145 EPA Water Quality Portal field readings (2011–2023). That is a typical value for the month, not a live reading.
How deep is Mary Lake?
- Mary Lake has a maximum depth of 46 feet and an average depth of 17.8 feet. The lake covers 189.97 acres.
What fish are in Mary Lake?
- Fish species found in Mary Lake include black crappie, bluegill, brown bullhead, common carp, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white sucker, yellow bullhead, yellow perch. Mary Lake is located in Wright County, Minnesota.
When does Mary Lake thaw?
- Mary Lake typically has ice-out around Apr 9. Ice typically forms around Dec 1. The open water season is approximately 236 days.
Are there boat ramps on Mary Lake?
- Mary Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Johnson Park. Public access is listed as yes.
Explore Mary Lake across LakeGrade
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Species activity outlook by water temperature and season
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Moderate nutrients, good water quality
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State Parks Near Mary Lake
Other Grade C Lakes in Minnesota
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Where this data comes from
161 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
MNPCA161 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)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
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