Blackduck Lake
Blackduck Lake in St. Louis County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 6.8 ft visibility. Phosphorus: 43 µg/L. Chlorophyll-a (algae): 23.3 µg/L. Maximum depth: 30 ft. Surface area: 1249.89 acres.
- Clarity
- 6.8 ft
- Typical in August
- 70°F
- Max depth
- 30 ft
- Area
- 1,250 acres
- Type
- Eutrophic
- Trend
- → Stable
- Public access
- Yes
- Ice-out
- Apr 18
- Open water
- 221 days
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Blackduck Lake →
Next lake in St. Louis County
Free interactive depth-contour map of Blackduck Lake, reaching a maximum surveyed depth of 30 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Blackduck Lake is a 1,250-acre productive, nutrient-rich eutrophic lake in St. Louis County, Minnesota with a maximum depth of 30 feet. Water quality is graded D based on 2 sampling years through 2025. The lake supports 8 documented fish species including black crappie, bluegill, and northern pike. Public access is available with 1 public boat landing. Compared to the 67 other monitored lakes in St. Louis County, Blackduck Lake ranks #66 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-23. 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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Moderate clarity, visible to about 6.8 ft. Phosphorus level: 43 µg/L. Chlorophyll-a: 23.3 µg/L. Trophic State Index: 56.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.8 ft | Not graded |
| Phosphorus | 43 µg/L | Poor |
| Chlorophyll-a (Algae) | 23.3 µg/L | Poor |
| Trophic State Index (TSI) | 56 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Blackduck Lake
Compare lakeside cabins, hotels, and vacation rentals near Blackduck 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Blackduck Lake are listed below.
Top-rated places to stay near Blackduck Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Blackduck Lake typically sits around 70°F at the surface in August. Summer average is about 68°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 135 field readings (2016–2025) via the EPA Water Quality Portal. See the full Blackduck Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 30 ft |
| Surface Area | 1,250 acres |
| Shoreline Length | 12.1 mi |
| Littoral Zone | 40% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Blackduck LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Blackduck Lake
DNR Fisheries Survey Summary
11 surveys on file from MN DNR Fisheries. Most recent: 2023-05-31 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Smallmouth Bass | 64.99 | 0.86 lb |
| Yellow Perch | 36.11 | 0.2 lb |
| Bluegill | 6.39 | 0.34 lb |
| White Sucker | 6.22 | 1.56 lb |
| Walleye | 4.97 | 2.5 lb |
| Pumpkinseed | 2.03 | 0.27 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.
Smallmouth Bass
Yellow Perch
Bluegill
White Sucker
From the 2023-05-31 survey
Black Duck Lake is located approximately 10 miles north of the city of Orr. Black Duck is a productive class 5 lake with 1,250 surface acres and a maximum depth of 30 feet. Approximately 498 acres (40%) are less than 15 feet deep. Secchi depth during the 2022 survey was 10 feet, but the lake is prone to algae blooms…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Blackduck Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — Black DuckFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Black Duck (1906)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — Black DuckPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.018 m/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (20 observations).
Estimated open water season: 221 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-19 (2012) | 2022-05-10 (2022) |
| Ice-In | 2019-11-11 (2019) | 2016-12-13 (2016) |
Most recent ice-out: 2023-05-07
EPA Impairment Status
Blackduck 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 MN69-0842-00 · Official waterbody report
County Ranking
Ranked #66 of 68 lakes in St. Louis County
Nearby Lakes in St. Louis County
Frequently asked questions about Blackduck Lake
What is the water quality grade for Blackduck Lake?
- Blackduck Lake in St. Louis County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 6.8 ft visibility. Phosphorus: 43 µg/L. Chlorophyll-a (algae): 23.3 µg/L. Maximum depth: 30 ft. Surface area: 1249.89 acres.
Is Blackduck Lake safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Blackduck Lake has a water quality grade of D (Nutrient-rich). Algae concentration (chlorophyll-a) is 23.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Blackduck Lake?
- Blackduck Lake typically sits around 70°F at the surface in August, from 135 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Blackduck Lake?
- Blackduck Lake has a maximum depth of 30 feet. The lake covers 1249.89 acres.
What fish are in Blackduck Lake?
- Fish species found in Blackduck Lake include black crappie, bluegill, northern pike, pumpkinseed, smallmouth bass, walleye, white sucker, yellow perch. Blackduck Lake is located in St. Louis County, Minnesota.
When does Blackduck Lake thaw?
- Blackduck Lake typically has ice-out around Apr 18. Ice typically forms around Nov 25. The open water season is approximately 221 days.
Are there boat ramps on Blackduck Lake?
- Blackduck Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Blackduck Lake. Public access is listed as yes.
Explore Blackduck Lake across LakeGrade
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Where this data comes from
91 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA91 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
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