Armstrong Lake
Armstrong Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 16.2 ft visibility. Maximum depth: 34 ft. Surface area: 382.34 acres.
- Clarity
- 16.2 ft
- Typical in August
- 69°F
- Max depth
- 34 ft
- Area
- 382 acres
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Mar 31
Next lake in St. Louis County
Why Armstrong 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 Armstrong 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.
Armstrong Lake is a 382-acre lake in St. Louis County, Minnesota with a maximum depth of 34 feet. Overall water quality is declining over recent sampling years. The lake supports 10 documented fish species including black crappie, bluegill, and largemouth bass. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-09-03. 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 Armstrong Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Crystal clear, you can see 16.2 ft down. Trophic State Index: 37.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 16.2 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 37 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Armstrong Lake
Compare lakeside cabins, hotels, and vacation rentals near Armstrong Lake in St. Louis 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 Armstrong Lake
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Water Temperature
Armstrong Lake typically sits around 69°F at the surface in August. Summer average is about 65°F. Usually warmest in Aug (about 69°F) and coldest in May (about 55°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 31 field readings (2016–2016) via the EPA Water Quality Portal. See the full Armstrong Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 34 ft |
| Surface Area | 382 acres |
| Shoreline Length | 4.5 mi |
| Littoral Zone | 27% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Armstrong LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Armstrong Lake
DNR Fisheries Survey Summary
8 surveys on file from MN DNR Fisheries. Most recent: 2021-08-09 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 24.60 | 0.17 lb |
| Largemouth Bass | 11.73 | 0.74 lb |
| IOD | 5.05 | — |
| Walleye | 3.43 | 3.21 lb |
| White Sucker | 3.34 | 2.27 lb |
| Northern Pike | 3.15 | 2.32 lb |
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
Walleye
White Sucker
From the 2021-08-09 survey
Armstrong Lake is a 382 acre lake located 10 miles west of Ely. It is accessed by a concrete ramp off Hwy 169. The lake has a maximum depth of 34 feet and clear water at the time of this survey. On August 9, 2021 the lake was thermally stratified with a surface temperature of 72 F and a bottom temperature of 54 F.…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Armstrong Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — ArmstrongFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Armstrong (1864)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — ArmstrongFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — ArmstrongPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.312 m/yr | 5 |
Ice Season
Historical ice data from Minnesota DNR (3 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2010-03-31 (2010) | 2015-05-14 (2015) |
Most recent ice-out: 2015-05-14
EPA Impairment Status
Armstrong 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 MN69-0278-00 · Official waterbody report
Graded lakes near Armstrong Lake
Armstrong Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in St. Louis County
Frequently asked questions about Armstrong Lake
What is the water quality grade for Armstrong Lake?
- Armstrong Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 16.2 ft visibility. Maximum depth: 34 ft. Surface area: 382.34 acres.
Is Armstrong Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Armstrong Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
What is the water temperature of Armstrong Lake?
- Armstrong Lake typically sits around 69°F at the surface in August, from 31 EPA Water Quality Portal field readings (2016–2016). That is a typical value for the month, not a live reading.
How deep is Armstrong Lake?
- Armstrong Lake has a maximum depth of 34 feet. The lake covers 382.34 acres.
What fish are in Armstrong Lake?
- Fish species found in Armstrong Lake include black crappie, bluegill, largemouth bass, northern pike, pumpkinseed, rock bass, smallmouth bass, walleye, white sucker, yellow perch. Armstrong Lake is located in St. Louis County, Minnesota.
When does Armstrong Lake thaw?
- Armstrong Lake typically has ice-out around Mar 31.
Are there boat ramps on Armstrong Lake?
- Armstrong Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Armstrong Lake. Public access is listed as yes.
Explore Armstrong Lake across LakeGrade
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Where this data comes from
72 measurements from 4 monitoring stations, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA72 samples · 2020–2023
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (4)
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
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