Connecticut lake · state assessment record
West Thompson Lake (Thompson)
Assessment decisions reported by Connecticut to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2008 reporting cycle.
- 189
- Assessed acres
- Lake, Freshwater
- Water type
This waterbody in one line
West Thompson Lake (Thompson), a lake in Connecticut, is assessed as not supporting one or more designated uses, with 3 listed impairment causes in the state's most recent Integrated Report cycle (2008). By assessed acreage it sits in the upper quartile by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (3 listed causes vs 23,610 assessed lakes). Aquatic life is assessed as not supporting.
- Not Supporting
- overall status
- P81
- Assessed size nationally
- P5
- Shorter cause list
- Not Supporting
- aquatic life
Assessment verdicts are the state agency's decisions as reported to EPA ATTAINS; PlainLakes renders them without modification.
A composite of this record's EPA ATTAINS designated-use verdicts, filed impairment count, and assessment currency, weighted and benchmarked against the national corpus of assessed active waterbodies. This is a water-quality standing, not a human-recreation or property-value judgment, and dimensions with no filed verdict drop out rather than count against the score.
West Thompson Lake (Thompson) against the ATTAINS register
Paragraphs are selected by this unit's percentiles and use matrix: different lakes lead with different dimensions. Figures are ATTAINS / portal register arithmetic, not advice.
The signature stat: cause-list length
The standout filed fact is cause-list length: 3 listed impairment causes, a longer list than 90% of assessed lake-type units (n=23,610). List length tracks how states sample and code, not a severity score.
Every filed use falls short
On the uses this filer ruled on, recreation, aquatic life, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
West Thompson Lake (Thompson): Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for West Thompson Lake (Thompson). Read the listed causes and any cleanup actions filed beside them before treating the overall status tile as a finished restoration story.
Large assessed unit
At 189.3 acres, West Thompson Lake (Thompson) clears the upper tercile of assessed lake-type units with an area on file (7,542 still larger). Size comparisons use the portal's deduplicated lake ranking population, not raw ATTAINS row counts.
Overall status: not supporting
The filer's overall status for West Thompson Lake (Thompson) is Not Supporting. That tile summarizes the assessment unit; the designated-use rows and cause list are the evidence behind it.
According to the U.S. Environmental Protection Agency's ATTAINS program, Connecticut carries 182 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to West Thompson Lake (Thompson) without modification. See our methodology for reporting-unit limits and gauge linking rules.
The record
Designated-use assessments
Fully Supporting and Not Supporting are the state's definitive verdicts; other entries mean the use was not conclusively assessed in this cycle. Connecticut filed its own confidence on the 2 definitive verdicts it rated: Good. That rating is the filer's, in EPA's own field, and EPA publishes no definition of the four words it offers.
| Designated use | Group | Verdict |
|---|---|---|
| Habitat for Fish, Other Aquatic Life and Wildlife | Aquatic-life or related | Not Supporting Filer confidence: Good |
| Recreation | Recreation | Not Supporting Filer confidence: Good |
| Fish Consumption | Fish-consumption or fishery | Insufficient Information Filer confidence: Good |
The record
Listed impairment causes
Causes the state listed as impairing designated uses of this lake, with the cycle each was first listed and the Clean Water Act action recorded against it.
| Cause | Affected uses | First listed | Cleanup standing |
|---|---|---|---|
| Algae | Recreation; Habitat for Fish, Other Aquatic Life and Wildlife | 1996 | TMDL priority: Low |
| Chlorophyll-a | Habitat for Fish, Other Aquatic Life and Wildlife; Recreation | 1996 | TMDL priority: Low |
| Nutrients | Habitat for Fish, Other Aquatic Life and Wildlife; Recreation | 1996 | TMDL priority: Low |
Probable sources named by the state
Each source below is listed under the cause the state filed it against, and carries the word the state filed with it — confirmed, or suspected.
- Algae
- Internal Nutrient Recycling (suspected) Municipal Point Source Discharges (suspected) Sources Outside State Jurisdiction or Borders (suspected) Agriculture (suspected)
- Chlorophyll-a
- Internal Nutrient Recycling (suspected) Municipal Point Source Discharges (suspected) Sources Outside State Jurisdiction or Borders (suspected) Agriculture (suspected)
- Nutrients
- Internal Nutrient Recycling (suspected) Municipal Point Source Discharges (suspected) Sources Outside State Jurisdiction or Borders (suspected) Agriculture (suspected)
Connecticut also recorded the source of at least one listing here as unknown, including for Algae, Chlorophyll-a, and Nutrients.
Reading the record
Where West Thompson Lake (Thompson) sits among peers
14% of Connecticut's lakes assessed this deeply also had no use supported
Connecticut ruled definitively on 2 designated uses at West Thompson Lake (Thompson) and found none of them supported. The dataset shows 74 Connecticut lakes judged to that same depth.
Connecticut's assessed lakes are most often judged on 2 uses, as this one was.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 42 | 53 | 0 | 0 | 0 |
| Mixed | Not possible | 11 | 5 | 1 | 0 |
| None supported | 16 | 10 (this record) | 1 | 0 | 0 |
Ringed cell: West Thompson Lake (Thompson). Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
West Thompson Lake (Thompson) is one of 182 lake-type waterbodies reported to EPA from Connecticut, and one of 97 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 189 assessed acres it ranks 7,543rd by assessed size among the 38,628 lakes the dataset carries an area for, counting a state’s repeated filings of one water once, behind 7,542 lakes with a larger one.
Open in the register
The state has not yet filed a definitive fish-consumption verdict for this record; that field populates when it reports it in a future Integrated Report cycle.
In context
Where West Thompson Lake (Thompson) sits nationally
Assessed size among U.S. lakes
Distribution of assessed acreage across ATTAINS lakes filed with an area, counting a state’s repeated filings of one water once
189 Top 19% larger than 81% of 38,628 lakes
lakes the dataset carries an area for, counting a state’s repeated filings of one water once, bucketed by value
Source EPA ATTAINS · Reporting cycles 1987–2026
Listed causes vs waterbodies carrying a verdict
How many impairment causes U.S. waterbodies with a reported verdict carry
3 Longer than most more listed causes than 90% of 23,610 waterbodies carrying a verdict
named waterbodies carrying a verdict, bucketed by value
Source EPA ATTAINS · Reporting cycles 1987–2026
In both charts each bar is a band and taller bars hold more waterbodies; the dashed line and filled bar mark West Thompson Lake (Thompson). Hover or tap any bar for its full count and share.
In context
Connecticut context
ATTAINS carries 182 lake-type waterbodies in Connecticut, 44 assessed as not supporting at least one use and 95 fully supporting. Among the 97 indexed units there, West Thompson Lake (Thompson) ranks 18th by listed-cause count (3 listed causes) and 31st by assessed size among the 97 with an area filed; it sits in the not-supporting set (44 statewide) . Its listed causes include Algae, Chlorophyll-a, and Nutrients, which also appear among Connecticut's most-filed impairment causes (led by Algae).
| Other large assessed lakes in Connecticut | Assessed acres |
|---|---|
| Candlewood, Lake (New Fairfield/Danbury/Sherman/New Milford) Fully Supporting | 5,086 |
| Lillinonah, Lake (Newtown/Southbury/Bridgewater/Brookfield) Not Supporting | 1,595 |
| Bantam Lake (Litchfield/Morris) Not Supporting | 955 |
| Colebrook River (Reservoir) Lake (Colebrook) Not Assessed | 852 |
| Pachaug Pond (Griswold) Fully Supporting | 837 |
| Saugatuck Reservoir (Weston/Easton/Redding) Fully Supporting | 823 |
Peers near West Thompson Lake (Thompson)'s size or cause load
Similar assessed acres
Nearest filed extents (189 acres here).
- Second Silver · 189 acres · MN
- Necedah Lake · 189 acres · WI
- Cynthia · 189 acres · MN
- Wright Patman Lake · 189 acres · TX
Similar cause load
Nearest listed-cause counts (3 here). Peers already in the acreage column are omitted.
- 67th St. Beach · 3 causes · IL
- Abiquiu Reservoir · 3 causes · NM
- Absecon Creek (AC Reserviors) (gage to SB) · 3 causes · NJ
- Absecon Creek (below gage) · 3 causes · NJ
What to do with this record
- Assessment verdicts are cycle-based, not real-time. For fish-consumption decisions, your state advisory program is the binding source. Consumption status guide
- Impairment listings follow the Clean Water Act 303(d) process; a listing is a regulatory finding, not a closure notice. 303(d) explained
PlainLakes renders state assessment decisions and federal gauge observations without modification. It does not issue advisories.
Assessment decisions on this page are rendered directly from state Integrated Report records in EPA's ATTAINS system; gauge figures are daily-value observations from the USGS National Water Information System, no number is typed in by an editor. Overall status, use verdicts, and causes are the state's reported decisions for assessment unit CT3700-00-2+L1_01. Counts and percentiles are computed across all lake-type records PlainLakes ingests from ATTAINS. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-08-17. Primary sources: EPA ATTAINS and USGS National Water Information System.