Prairie Lake
Prairie Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 5 ft visibility. Maximum depth: 47 ft. Surface area: 794.33 acres.
- Clarity
- 5 ft
- Max depth
- 47 ft
- Area
- 794 acres
- Trend
- → Stable
- Public access
- Yes
- Ice-out
- Apr 21
- Open water
- 222 days
Next lake in St. Louis County
Why Prairie 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 Prairie 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.
Prairie Lake is a 794-acre lake in St. Louis County, Minnesota with a maximum depth of 47 feet. The lake supports 15 documented fish species including black crappie, bluegill, and bowfin (dogfish). Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-04. 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 Prairie Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Murky, only visible to about 5 ft. Trophic State Index: 54.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 54 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Prairie Lake
Compare lakeside cabins, hotels, and vacation rentals near Prairie 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 Prairie Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Prairie Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was low (7,870 cells/mL) on May 16, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 47 ft |
| Surface Area | 794 acres |
| Shoreline Length | 8.2 mi |
| Littoral Zone | 34% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Prairie LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Prairie Lake
DNR Fisheries Survey Summary
8 surveys on file from MN DNR Fisheries. Most recent: 2025-08-13 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| MTS | 47.25 | — |
| JND | 20.43 | — |
| Yellow Perch | 16.03 | 0.16 lb |
| GOS | 12.44 | — |
| CNM | 11.11 | — |
| Walleye | 6.33 | 1.18 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.
Yellow Perch
Walleye
From the 2025-08-13 survey
A targeted survey of nearshore fish species in Prairie Lake was conducted on August 13th-20th, 2025, by Lake Biological Monitoring and Assessment (LBMA) program staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing, mini-fyke nets, and seining with a 50-foot or…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Prairie Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — PrairieFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Prairie (1873)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — PrairieFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — PrairiePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.011 m/yr | 4 |
Ice Season
Historical ice data from Minnesota DNR (6 observations).
Estimated open water season: 222 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2015-04-12 (2015) | 2008-04-30 (2008) |
| Ice-In | 2018-11-19 (2018) | 2007-11-29 (2007) |
Most recent ice-out: 2015-04-12
EPA Impairment Status
Prairie Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MN69-0848-00 · Official waterbody report
Graded lakes near Prairie Lake
Prairie Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in St. Louis County
Frequently asked questions about Prairie Lake
What is the water quality grade for Prairie Lake?
- Prairie Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 5 ft visibility. Maximum depth: 47 ft. Surface area: 794.33 acres.
Is Prairie Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Prairie 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 Prairie Lake?
- Prairie Lake has a maximum depth of 47 feet. The lake covers 794.33 acres.
What fish are in Prairie Lake?
- Fish species found in Prairie Lake include black crappie, bluegill, bowfin (dogfish), brown bullhead, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, shorthead redhorse, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Prairie Lake is located in St. Louis County, Minnesota.
When does Prairie Lake thaw?
- Prairie Lake typically has ice-out around Apr 21. Ice typically forms around Nov 29. The open water season is approximately 222 days.
Does Prairie Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Prairie Lake (clouds, ice, or an off-season gap). The most recent reading was low (7,870 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Prairie Lake?
- Prairie Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Prairie Lake. Public access is listed as yes.
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Where this data comes from
38 measurements from 3 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
MNPCA38 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (3)
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