Massachusetts lake · state assessment record
Quabbin Reservoir
Assessment decisions reported by Massachusetts to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2026 reporting cycle, a cycle that is open for public comment.
- 24,010
- Assessed acres
- Lake, Freshwater
- Water type
This waterbody in one line
Quabbin Reservoir, a lake in Massachusetts, is assessed as not supporting one or more designated uses, with 2 listed impairment causes in the state's most recent Integrated Report cycle (2026), a cycle that is open for public comment. By assessed acreage it sits among the largest 1% of assessed lakes nationally (38,628 lakes with a filed area); its impairment list is among the longest nationally (2 listed causes vs 23,610 assessed lakes). Aquatic life is assessed as not supporting. Fish consumption is assessed as not supporting.
- Not Supporting
- overall status
- P100
- Assessed size nationally
- P10
- 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.
Quabbin Reservoir 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: assessed size
The number that most separates Quabbin Reservoir nationally is assessed size: 24,010 acres, larger than 100% of the 38,628 lake-type units with an area on file.
Not one verdict, several
This record splits: Not Supporting on fish consumption, aquatic life, Fully Supporting on recreation. The divergence is inside the designated-use matrix, not a single all-or-nothing label.
Quabbin Reservoir: Category 4A reading
Category 4A means a TMDL (or equivalent) is already approved for the impairment on Quabbin Reservoir. The remaining work is implementation and tracking, read the cleanup-standing and cause rows for what the state already committed to address.
Longer than most cause lists
2 listed causes puts this unit above 80% of assessed lake-type records by list length. Treat that as a coding-and-sampling signal: states that split pollutants finely mint longer lists without proving worse water.
Overall status: not supporting
The filer's overall status for Quabbin Reservoir 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, Massachusetts carries 1,191 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Quabbin Reservoir 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. For the definitive verdicts on this record, Massachusetts filed the assessment basis as Monitored Data. Those are EPA's own words, not PlainLakes' summary of them.
| Designated use | Group | Verdict |
|---|---|---|
| Fish Consumption | Fish-consumption or fishery | Not Supporting |
| Fish, Other Aquatic Life and Wildlife | Aquatic-life or related | Not Supporting |
| Primary Contact Recreation | Recreation | Fully Supporting |
| Secondary Contact Recreation | Recreation | Fully Supporting |
| Aesthetic | Other | Not Assessed |
| Public Water Supply | Drinking-water supply designation | Not Assessed |
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 |
|---|---|---|---|
| Mercury in Fish Tissue | Fish Consumption | 1992 | TMDL approved |
| Non-Native Aquatic Plants | Fish, Other Aquatic Life and Wildlife | 2010 | None reported |
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.
- Mercury in Fish Tissue
- Atmospheric Deposition (suspected)
- Non-Native Aquatic Plants
- Introduction of Non-Native Organisms (Accidental or Intentional) (confirmed)
Massachusetts also recorded the source of at least one listing here as unknown, including for Mercury in Fish Tissue.
Reading the record
Quabbin Reservoir: Category 4A reading
4A Category 4A: impaired, TMDL completed
Massachusetts filed this assessment unit as Category 4A: impaired, with a pollutant-budget TMDL already completed under 303(d). The listing remains an impairment finding; the plan is on file rather than still awaiting write-up.
Scale and rank
Quabbin Reservoir is one of 1,191 lake-type waterbodies reported to EPA from Massachusetts, and one of 678 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 24,010 assessed acres it ranks 130th 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 129 lakes with a larger one.
Why no water-level record
Quabbin Reservoir has no daily USGS water-level or reservoir-storage series on this page because NWIS lists a lake monitoring site named for the waterbody, but the site is not active, and PlainLakes ingests only the active inventory, so there is no series to attach. How PlainLakes links gauges.
In context
Where Quabbin Reservoir 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
24,010 Top 1% larger than 99%+ 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
2 Longer than most more listed causes than 80% 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 Quabbin Reservoir. Hover or tap any bar for its full count and share.
In context
Massachusetts context
ATTAINS carries 1,191 lake-type waterbodies in Massachusetts, 678 assessed as not supporting at least one use and 40 fully supporting. Among the 678 indexed units there, Quabbin Reservoir ranks 234th by listed-cause count (2 listed causes) and 1st by assessed size among the 678 with an area filed; it sits in the not-supporting set (678 statewide) . Its listed causes include Mercury in Fish Tissue and Non-Native Aquatic Plants, which also appear among Massachusetts's most-filed impairment causes (led by Mercury in Fish Tissue).
| Other large assessed lakes in Massachusetts | Assessed acres |
|---|---|
| Wachusett Reservoir Not Supporting | 3,962 |
| Assawompset Pond Not Assessed | 2,034 |
| North Watuppa Pond Not Supporting | 1,728 |
| Long Pond Not Supporting | 1,728 |
| South Watuppa Pond Not Supporting | 1,473 |
| Webster Lake Not Supporting | 1,275 |
Peers near Quabbin Reservoir's size or cause load
Similar assessed acres
Nearest filed extents (24,010 acres here).
- American Falls Reservoir (Snake River) Tribal Waters · 23,785 acres · ID
- Stockton Lake · 23,680 acres · MO
- Grays Lake · 23,678 acres · ID
- Eagle Lake (Lassen County) · 24,377 acres · CA
Similar cause load
Nearest listed-cause counts (2 here). Peers already in the acreage column are omitted.
- 12th St. Beach · 2 causes · IL
- 31st St. Beach · 2 causes · IL
- 49th St. Beach · 2 causes · IL
- 57th St. Beach · 2 causes · IL
What to do with this record
- The fish-consumption use is assessed as not supporting. Before eating fish from this lake, check your state fish-advisory program for species-specific meal limits. 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 MA36129. 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.