St Mary'S Lake
St Mary'S Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 15 ft visibility. Maximum depth: 44 ft. Surface area: 234.16 acres.
- Clarity
- 15 ft
- Max depth
- 44 ft
- Area
- 234 acres
- Trend
- ↓ Declining
- Public access
- No
- Ice-out
- Apr 24
- Open water
- 212 days
Next lake in St. Louis County
Why St Mary'S Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For St Mary'S Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
St Mary'S Lake is a 234-acre lake in St. Louis County, Minnesota with a maximum depth of 44 feet. Overall water quality is declining over recent sampling years. The lake supports 14 documented fish species including black crappie, bluegill, and brown bullhead. No public access — the lake is private or restricted.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-08-14. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for St Mary'S Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Crystal clear, you can see 15 ft down. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 15 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near St Mary'S Lake
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Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 44 ft |
| Surface Area | 234 acres |
| Shoreline Length | 4.1 mi |
| Littoral Zone | 33% |
| Public Access | No |
Fish Species
Click a species to see every graded lake where it is documented.
Fishing St Mary'S Lake
DNR Fisheries Survey Summary
6 surveys on file from MN DNR Fisheries. Most recent: 2025-07-21 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 26.00 | 0.12 lb |
| Largemouth Bass | 9.80 | 0.76 lb |
| Pumpkinseed | 9.71 | 0.19 lb |
| BNS | 5.70 | — |
| Green Sunfish | 5.67 | 0.15 lb |
| Fathead Minnow | 5.40 | — |
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
Largemouth Bass
Pumpkinseed
Green Sunfish
From the 2025-07-21 survey
St. Mary's is a 234-acre lake located 2 miles south of Eveleth off the Miller Trunk Road. It shares much in common with Armstrong, Bass (Biwabik), and Ely lakes in the Tower Area. The water is clear, Secchi visibility is 13 feet, and the lake is up to 44 feet deep. St. Mary's was thermally stratified on 07/21, with a…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for St Mary'S Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — St. Mary'sFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — St. Mary's (1772)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — St. Mary'sFish 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 | -0.138 m/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (17 observations).
Estimated open water season: 212 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2017-04-09 (2017) | 2023-05-05 (2023) |
| Ice-In | 2018-11-18 (2018) | 2015-11-29 (2015) |
Most recent ice-out: 2023-05-05
EPA Impairment Status
St Mary'S Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN69-0651-00 · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of St Mary'S Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Eveleth WwtpEveleth · 2.4 mi away · NPDES MN0023337Recent violation
- Eveleth Mines Llc Dba EvtacEveleth · 1.6 mi away · NPDES MN0044946
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.
Graded lakes near St Mary'S Lake
St Mary'S Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in St. Louis County
Frequently asked questions about St Mary'S Lake
What is the water quality grade for St Mary'S Lake?
- St Mary'S Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 15 ft visibility. Maximum depth: 44 ft. Surface area: 234.16 acres.
Is St Mary'S Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. St Mary'S Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
How deep is St Mary'S Lake?
- St Mary'S Lake has a maximum depth of 44 feet. The lake covers 234.16 acres.
What fish are in St Mary'S Lake?
- Fish species found in St Mary'S Lake include black crappie, bluegill, brown bullhead, cisco species, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. St Mary'S Lake is located in St. Louis County, Minnesota.
When does St Mary'S Lake thaw?
- St Mary'S Lake typically has ice-out around Apr 24. Ice typically forms around Nov 22. The open water season is approximately 212 days.
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Where this data comes from
14 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA14 samples · 2020–2024
Analytical methods
- Field measurement/observation, generic method
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
Ice data from Minnesota DNR Climate