Johnson Lake
Johnson Lake in St. Louis County, Minnesota has a water quality grade of C (Fair). Water clarity: 3 ft visibility. Phosphorus: 33 µg/L. Chlorophyll-a (algae): 9.8 µg/L. Maximum depth: 18 ft. Surface area: 455.98 acres.
- Clarity
- 3 ft
- Typical in August
- 70°F
- Max depth
- 18 ft
- Area
- 456 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in St. Louis County
Johnson Lake is a 456-acre productive, nutrient-rich eutrophic lake in St. Louis County, Minnesota with a maximum depth of 18 feet. Water quality is graded C based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 11 documented fish species including black bullhead, black crappie, and bluegill. Public access is available. Compared to the 67 other monitored lakes in St. Louis County, Johnson Lake ranks #50 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-15. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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)
Very murky, less than 3 ft of visibility. Phosphorus level: 33 µg/L. Chlorophyll-a: 9.8 µg/L. Trophic State Index: 56.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 33 µg/L | Fair |
| Chlorophyll-a (Algae) | 9.8 µg/L | Fair |
| Trophic State Index (TSI) | 56 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Johnson Lake
Compare lakeside cabins, hotels, and vacation rentals near Johnson 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.
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Water Temperature
Johnson Lake typically sits around 70°F at the surface in August. Summer average is about 69°F. Usually warmest in Jul (about 70°F) and coldest in Oct (about 52°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 39 field readings (2023–2025) via the EPA Water Quality Portal. See the full Johnson Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 18 ft |
| Surface Area | 456 acres |
| Shoreline Length | 10.6 mi |
| Littoral Zone | 93% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Johnson Lake
DNR Fisheries Survey Summary
10 surveys on file from MN DNR Fisheries. Most recent: 2022-06-06 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 5.54 | 0.22 lb |
| Black Bullhead | 5.49 | 0.41 lb |
| Black Crappie | 4.10 | 0.29 lb |
| White Sucker | 2.81 | 2.04 lb |
| Northern Pike | 2.67 | 2.28 lb |
| Yellow Perch | 1.72 | 0.11 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
Black Bullhead
Black Crappie
White Sucker
From the 2022-06-06 survey
Johnson Lake is located approximately 6 miles south of Ely in the Superior National Forest. The rolling shoreline is forested in a pine-hardwood mix and is lightly developed by area standards. Maximum depth is 19 feet and much of the lake is shallower than 15 feet. A heavy bog stain limits water clarity, which was…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Johnson Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — JohnsonFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Johnson (1884)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — JohnsonFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — JohnsonPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.04 m/yr | 3 |
EPA Impairment Status
Johnson 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 MN69-0117-00 · Official waterbody report
County Ranking
Ranked #50 of 68 lakes in St. Louis County
Nearby Lakes in St. Louis County
Frequently asked questions about Johnson Lake
What is the water quality grade for Johnson Lake?
- Johnson Lake in St. Louis County, Minnesota has a water quality grade of C (Fair). Water clarity: 3 ft visibility. Phosphorus: 33 µg/L. Chlorophyll-a (algae): 9.8 µg/L. Maximum depth: 18 ft. Surface area: 455.98 acres.
Is Johnson Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Johnson Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 9.8 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Johnson Lake?
- Johnson Lake typically sits around 70°F at the surface in August, from 39 EPA Water Quality Portal field readings (2023–2025). That is a typical value for the month, not a live reading.
How deep is Johnson Lake?
- Johnson Lake has a maximum depth of 18 feet. The lake covers 455.98 acres.
What fish are in Johnson Lake?
- Fish species found in Johnson Lake include black bullhead, black crappie, bluegill, burbot, largemouth bass, northern pike, pumpkinseed, rock bass, walleye, white sucker, yellow perch. Johnson Lake is located in St. Louis County, Minnesota.
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High nutrients, frequent algae, reduced clarity
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Where this data comes from
37 measurements from 1 monitoring station, 2023–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA37 samples · 2023–2025
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder