West Thompson Lake
Windham County, Connecticut200 acresView mapDirections
CT DEEP publishes the water-quality measurements for West Thompson Lake. Here is what has been measured.
- Eutrophic
- Impaired · Algal growth
- Limited data
West Thompson Lake in Windham County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Water clarity: 5.3 ft visibility. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 8.5 µg/L. Surface area: 200 acres.
West Thompson Lake is a 200-acre productive, nutrient-rich eutrophic lake in Windham County, Connecticut. Compared to the 2 other monitored lakes in Windham County, West Thompson Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2022-10-20. Methodology: how these readings are compared.
Swimming conditions
Readings onlyRecreation use not supported
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. West Thompson Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether West Thompson Lake is safe to swim in today is a call for the Connecticut Department of Energy and Environmental Protection and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for West Thompson Lake
These are the measurements CT DEEP publishes for West Thompson Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.3 ft. Phosphorus 22 µg/L. Chlorophyll-a 8.5 µg/L. TSI 51.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 22µg/L | Fair GoodFairPoor |
| Chlorophyll-a (algae) | 8.5µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 51 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about West Thompson Lake
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Lake Details
Surface area
200 acres
No bathymetric survey has been published for West Thompson Lake, so its depth is not documented here.
Stays via Stay22
Stays near West Thompson Lake
Compare lakeside cabins, hotels, and vacation rentals near West Thompson Lake in Windham County, Connecticut — 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 readings cover nutrients and algae, not lodging. Cabins and rentals around West Thompson Lake are listed below.
Top-rated places to stay near West Thompson Lake
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Fishing West Thompson Lake
Reservoir Info (USACE NID)
West Thompson Lake is a man-made reservoir impounded by the West Thompson Dam (completed 1965), built primarily for flood risk reduction on the Quinebaug River; gravity-type dam, 70 ft tall and 2,550 ft long.
- Surface area
- 200 ac
- Normal storage
- 1,200 ac-ft
- Max storage
- 47,800 ac-ft
- Drainage area
- 174 sq mi
- Hazard class
- High
- Owner
- USACE - New England District
All listed purposes: Flood Risk Reduction;Recreation.
Source: USACE National Inventory of Dams, NID ID CT00502 · Operator website
EPA Impairment Status
West Thompson Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Aquatic life, Recreation.
Source: EPA ATTAINS assessment unit CT3700-00-2+L1_01 · Official waterbody report
Nearby Lakes in Windham County
Frequently asked questions about West Thompson Lake
Where is West Thompson Lake?
- West Thompson Lake is a lake in Windham County, Connecticut. Its water-quality measurements are published by CT DEEP and shown on this page as reported.
What is the water quality of West Thompson Lake?
- West Thompson Lake in Windham County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Water clarity: 5.3 ft visibility. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 8.5 µg/L. Surface area: 200 acres.
Is West Thompson Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. West Thompson Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Explore West Thompson Lake across LakeQuality
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Where this data comes from
27 measurements from 1 monitoring station, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- USGS Connecticut Water Science Center
USGS-CT27 samples · 2022
Analytical methods
- Secchi disk method
- P, wu, WCA, persulfate CF color
- Phosphorus, wu, microKJ ASF, H+
- Plant pigments, sonication & 445
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database