Thompson Lake
Thompson Lake in Sherburne County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 10 ft visibility. Maximum depth: 22 ft. Surface area: 84.34 acres.
- Clarity
- 10 ft
- Typical in August
- 80°F
- Max depth
- 22 ft
- Area
- 84 acres
- Trend
- ↓ Declining
- Public access
- No
Next lake in Sherburne 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 84-acre lake in Sherburne County, Minnesota with a maximum depth of 22 feet (10-foot average). Overall water quality is declining over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-26. 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 Thompson Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Good clarity, visible to about 10 ft. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Thompson Lake
Compare lakeside cabins, hotels, and vacation rentals near Thompson Lake in Sherburne 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
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Water Temperature
Thompson Lake typically sits around 80°F at the surface in August. Summer average is about 79°F. Usually warmest in Jul (about 81°F) and coldest in May (about 67°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 71 field readings (2010–2025) via the EPA Water Quality Portal. See the full Thompson Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 22 ft |
| Average Depth | 9.6 ft |
| Surface Area | 84 acres |
| Shoreline Length | 2.1 mi |
| Littoral Zone | 75% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fishing Thompson Lake
DNR Fisheries Survey Summary
2 surveys on file from MN DNR Fisheries. Most recent: 1990-07-02 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 78.31 | 0.18 lb |
| Northern Pike | 8.75 | 1.27 lb |
| Hybrid Sunfish | 6.63 | 0.11 lb |
| Pumpkinseed | 5.17 | 0.14 lb |
| Brown Bullhead | 2.38 | 0.54 lb |
| Black Crappie | 2.00 | 0.25 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
From the 1990-07-02 survey
Thompson Lake is an 84-acre lake in Sherburne County four miles northwest of the City of Big Lake. The lake has a maximum depth of 22 feet with an average depth of 10 feet. A standard survey was completed in 1990 to update fisheries data last collected in 1978. Northern Pike were sampled at a rate of 7.5/gill net,…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Thompson Lake. 1 report 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
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.118 m/yr | 6 |
EPA Impairment Status
Thompson Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN71-0081-00 · Official waterbody report · Matched by proximity (2.08 km)
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Thompson Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 1 facility has a reported Clean Water Act violation in the past three years.
- Becker Wwtp - MunicipalBecker · 4.9 mi away · NPDES MN0025666MajorRecent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Graded lakes near Thompson Lake
Thompson Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Sherburne County
Frequently asked questions about Thompson Lake
What is the water quality grade for Thompson Lake?
- Thompson Lake in Sherburne County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 10 ft visibility. Maximum depth: 22 ft. Surface area: 84.34 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.
What is the water temperature of Thompson Lake?
- Thompson Lake typically sits around 80°F at the surface in August, from 71 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Thompson Lake?
- Thompson Lake has a maximum depth of 22 feet and an average depth of 9.6 feet. The lake covers 84.34 acres.
Explore Thompson Lake across LakeGrade
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Where this data comes from
101 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA101 samples · 2020–2025
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder