Thompson Lake
Thompson Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3.3 ft visibility. Phosphorus: 54 µg/L. Chlorophyll-a (algae): 36 µg/L. Maximum depth: 8 ft. Surface area: 8.08 acres.
- Clarity
- 3.3 ft
- Typical in August
- 74°F
- Max depth
- 8 ft
- Area
- 8 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- No
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Thompson Lake →
Next lake in Dakota County
Thompson Lake is a 8-acre productive, nutrient-rich eutrophic lake in Dakota County, Minnesota with a maximum depth of 8 feet. Water quality is graded F based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 44 other monitored lakes in Dakota County, Thompson Lake ranks #34 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-27. Grade methodology: LakeGrade methodology.
Watch Thompson Lake water quality
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Swimming Safety
Grade onlyBacteria D
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.
Based on E. coli testing, Thompson Lake frequently exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 18.2% of 11 samples across 2 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Minnesota’s current beach and health-department advisories before swimming.
Water Quality Grade: F (Algae-prone)
Very murky, less than 3.3 ft of visibility. Phosphorus level: 54 µg/L. Chlorophyll-a: 36 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.3 ft | Not graded |
| Phosphorus | 54 µg/L | Poor |
| Chlorophyll-a (Algae) | 36 µg/L | Poor |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Thompson Lake
Compare lakeside cabins, hotels, and vacation rentals near Thompson Lake in Dakota 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 Thompson Lake are listed below.
Top-rated places to stay near Thompson Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Thompson Lake typically sits around 74°F at the surface in August. Summer average is about 75°F. Usually warmest in Jul (about 79°F) and coldest in Jan (about 33°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 67 field readings (2011–2025) via the EPA Water Quality Portal. See the full Thompson Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 8 ft |
| Surface Area | 8 acres |
| Shoreline Length | 0.5 mi |
| Littoral Zone | 87% |
| Public Access | No |
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.
DNR Fisheries Survey Summary
3 surveys on file from MN DNR Fisheries. Most recent: 2013-06-03 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 42.67 | 0.12 lb |
| Black Bullhead | 37.30 | 0.15 lb |
| Green Sunfish | 8.27 | 0.1 lb |
| Pumpkinseed | 3.70 | 0.14 lb |
| Hybrid Sunfish | 2.73 | 0.17 lb |
| Black Crappie | 2.10 | 0.48 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
Green Sunfish
Pumpkinseed
From the 2013-06-03 survey
Thompson Lake is a small 10 acre lake located in Thompson County Park (Dakota County Parks) within the city limits of West St. Paul. The lake has a maximum depth of eight feet and receives primarily stormwater inputs from the 169 acre surrounding watershed. A spillway outlet structure maintains the water level and…
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
- —Fish Stocking History — ThompsonFish Stocking History · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.38 m/yr | 2 |
Reservoir Info (USACE NID)
Thompson Lake is a man-made reservoir impounded by the Kaposia Park (completed 1932), built primarily for flood risk reduction on the Mississippi River-TR; earth-type dam, 79 ft tall.
- Max storage
- 180 ac-ft
- Drainage area
- 1.5 sq mi
- Hazard class
- Significant
- Owner
- City of South St. Paul
Source: USACE National Inventory of Dams, NID ID MN00675 · Operator website · Matched by proximity (0.99 km)
EPA Impairment Status
Thompson 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 MN19-0048-00 · Official waterbody report
County Ranking
Ranked #34 of 45 lakes in Dakota County
Nearby Lakes With Higher Grades
Thompson Lake holds Grade F. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Dakota County
Frequently asked questions about Thompson Lake
What is the water quality grade for Thompson Lake?
- Thompson Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3.3 ft visibility. Phosphorus: 54 µg/L. Chlorophyll-a (algae): 36 µg/L. Maximum depth: 8 ft. Surface area: 8.08 acres.
Is Thompson Lake safe to swim in?
- Based on E. coli testing, Thompson Lake frequently exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 18.2% of 11 samples across 2 seasons. That works out to a bacteria swim-safety grade of D — a historical summary of past testing, not a current reading. Thompson Lake has a water quality grade of F (Algae-prone). Bacteria levels can spike quickly after heavy rain, so always check Minnesota's current beach and health-department advisories before you swim.
What is the water temperature of Thompson Lake?
- Thompson Lake typically sits around 74°F at the surface in August, from 67 EPA Water Quality Portal field readings (2011–2025). That is a typical value for the month, not a live reading.
How deep is Thompson Lake?
- Thompson Lake has a maximum depth of 8 feet. The lake covers 8.08 acres.
Explore Thompson Lake across LakeGrade
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Dakota County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Minnesota River Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Thompson Lake
Other Grade F Lakes in Minnesota
Eutrophic Lakes in Minnesota
Where this data comes from
41 measurements from 1 monitoring station, 2024–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA41 samples · 2024–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- Analysis of Chlorophyll in Periphyton and Plankton
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 details from Minnesota DNR LakeFinder