Thompson Lake
Dakota County, MinnesotaLimited DataEutrophic
On the LakeGrade rubric Thompson Lake fails the cutoffs — a TSI of 62 and persistent algal pressure put it in the bottom tier.
A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. Thompson Lake is a shallow lake at 8 ft maximum depth, which means it warms quickly, mixes constantly, and amplifies nutrient inputs. The lake is compact at 8 acres, with 0.5 miles of shoreline and little volume to buffer nutrient inputs. Within Dakota County's 36 graded lakes, Thompson Lake ranks 26 — below the local median, though not at the bottom.
Eurasian watermilfoil is established at Thompson Lake, which can dampen recreational access and pressure the native plant community. The state fisheries records do not list documented species for Thompson Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Thompson Lake — most use is by shoreline residents and their guests. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-23. Grade methodology: LakeGrade methodology.
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 2.8 ft of visibility. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.8 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 8 ft |
| Surface Area | 8.08 acres |
| Shoreline Length | 0.5 mi |
| Littoral Zone | 87% |
| Public Access | No |
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Location
County Ranking
Ranked #26 of 36 lakes in Dakota County
Cleaner Lakes Within 30 Miles
Thompson Lake holds Grade F. 4 nearby lakes hold higher grades.
Nearby Lakes in Dakota County
More Minnesota Lake Rankings
State Parks Near Thompson Lake
Other Grade F Lakes in Minnesota
Eutrophic Lakes in Minnesota
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.
- —Fisheries Lake Survey — ThompsonFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — ThompsonFish Stocking History · MN DNR LakeFinder
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
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Lake details from Minnesota DNR LakeFinder
Most recent sample: 2024-10-23
Monitoring stations: 1