Thompson Lake
Thompson Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 3 ft visibility. Maximum depth: 9 ft. Surface area: 207.17 acres.
- Clarity
- 3 ft
- Max depth
- 9 ft
- Area
- 207 acres
- Trend
- → Stable
- Public access
- No
- Ice-out
- Apr 23
- Open water
- 209 days
Next lake in St. Louis County
Why Thompson 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 Thompson 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.
Thompson Lake is a 207-acre lake in St. Louis County, Minnesota with a maximum depth of 9 feet. The lake supports 8 documented fish species including black bullhead, black crappie, and bluegill. No public access — the lake is private or restricted.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-10-17. Grade methodology: LakeGrade methodology.
Watch Thompson Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Thompson Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Very murky, less than 3 ft of visibility. Trophic State Index: 61.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 61 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Thompson Lake
Compare lakeside cabins, hotels, and vacation rentals near Thompson 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 Thompson Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 9 ft |
| Surface Area | 207 acres |
| Shoreline Length | 3.9 mi |
| Littoral Zone | 100% |
| Public Access | No |
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 Thompson Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Source: USGS Nonindigenous Aquatic Species (NAS) Database. Hover a chip to see scientific name, ecological context, status, and first-observed year.
DNR Fisheries Survey Summary
2 surveys on file from MN DNR Fisheries. Most recent: 2000-09-11 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 68.88 | 0.21 lb |
| Pumpkinseed | 4.76 | 0.19 lb |
| White Sucker | 3.59 | 3.41 lb |
| Northern Pike | 2.17 | 2.21 lb |
| Yellow Perch | 1.86 | 0.16 lb |
| Black Crappie | 1.64 | 0.29 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.
Black Bullhead
Pumpkinseed
White Sucker
Northern Pike
From the 2000-09-11 survey
Results from the 2000 lake survey indicate that Thompson Lake is currently comprised of northern pike, yellow perch, black crappie, pumpkinseed sunfish, and black bullhead. There is no established boat access but walk-in access can be gained through county tax forfeit land on the south side of the lake. Thompson Lake…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Thompson Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — ThompsonFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Thompson (0486)Aquatic Plant Report · MN DNR LakeFinder
Water Quality Trend: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.013 m/yr | 4 |
Ice Season
Historical ice data from Minnesota DNR (23 observations).
Estimated open water season: 209 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2017-04-12 (2017) | 2022-05-07 (2022) |
| Ice-In | 2003-11-08 (2003) | 2006-12-01 (2006) |
Most recent ice-out: 2023-05-03
Nearby Lakes in St. Louis County
Frequently asked questions about Thompson Lake
What is the water quality grade for Thompson Lake?
- Thompson Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 3 ft visibility. Maximum depth: 9 ft. Surface area: 207.17 acres.
Is Thompson Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Thompson 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 Thompson Lake?
- Thompson Lake has a maximum depth of 9 feet. The lake covers 207.17 acres.
What fish are in Thompson Lake?
- Fish species found in Thompson Lake include black bullhead, black crappie, bluegill, largemouth bass, northern pike, pumpkinseed, white sucker, yellow perch. Thompson Lake is located in St. Louis County, Minnesota.
When does Thompson Lake thaw?
- Thompson Lake typically has ice-out around Apr 23. Ice typically forms around Nov 18. The open water season is approximately 209 days.
Explore Thompson Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in St. Louis County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Lake Vermilion Area area
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Lake Superior Basin (MN+WI), ranked by water quality
Lakes in the Rainy Lake Watershed, ranked by water quality
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
Other Lakes in Minnesota
Eutrophic Lakes in Minnesota
Where this data comes from
63 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA63 samples · 2020–2023
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate