New Hampshire reservoir · state assessment record
Squam Lake
Assessment decisions reported by New Hampshire to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2024 reporting cycle.
- 6,774
- Assessed acres
- Lake / Reservoir / Pond
- Water type
This waterbody in one line
Squam Lake, a reservoir in New Hampshire, is assessed as not supporting one or more designated uses, with 5 listed impairment causes in the state's most recent Integrated Report cycle (2024). 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 (5 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
- P99
- Assessed size nationally
- P1
- 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.
Squam Lake 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 Squam Lake nationally is assessed size: 6,774 acres, larger than 99% of the 38,628 lake-type units with an area on file.
Longer than most cause lists
5 listed causes puts this unit above 97% 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.
Every ruled-on use is not supporting
On the uses this filer ruled on, fish consumption, aquatic life, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
Squam Lake: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Squam Lake. Read the listed causes and any cleanup actions filed beside them before treating the overall status tile as a finished restoration story.
Overall status: not supporting
The filer's overall status for Squam Lake 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, New Hampshire carries 2,786 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Squam Lake 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. The latest monitoring New Hampshire filed against this record runs through 2023. For the definitive verdicts on this record, New Hampshire filed the assessment basis as Monitored Data. Those are EPA's own words, not PlainLakes' summary of them.
| Designated use | Group | Verdict |
|---|---|---|
| Aquatic Life Integrity | Aquatic-life or related | Not Supporting |
| Fish Consumption | Fish-consumption or fishery | Not Supporting |
| Potential Drinking Water Supply | Drinking-water supply designation | Fully Supporting |
| Primary Contact Recreation | Recreation | Insufficient Information |
| Secondary Contact Recreation | Recreation | Insufficient Information |
The record
Listed impairment causes
Causes the state listed as impairing designated uses of this reservoir, with the cycle each was first listed and the Clean Water Act action recorded against it.
| Cause | Affected uses | First listed | Cleanup standing |
|---|---|---|---|
| Mercury - Fish Consumption Advisory | Fish Consumption | 2002 | TMDL approved |
| Dissolved Oxygen | Aquatic Life Integrity | 2010 | TMDL priority: Low |
| Dissolved Oxygen Saturation | Aquatic Life Integrity | 2010 | TMDL priority: Low |
| pH | Aquatic Life Integrity | 2010 | TMDL priority: Low |
| PCBs - Fish Consumption Advisory | Fish Consumption | 2020 | TMDL priority: Low |
Reading the record
Where Squam Lake sits among peers
436 of 436 New Hampshire lakes assessed this deeply also came out mixed (every lake judged to this depth, so the outcome does not set this record apart)
New Hampshire ruled definitively on 3 designated uses at Squam Lake and found 2 of 3 not supported. The dataset shows 436 New Hampshire lakes judged to that same depth.
New Hampshire's assessed lakes are most often judged on 2 uses; this one was judged on 3.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 0 | 0 | 0 | 0 | 0 |
| Mixed | Not possible | 2k | 436 (this record) | 297 | 85 |
| None supported | 1 | 0 | 0 | 0 | 0 |
Ringed cell: Squam Lake. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Squam Lake is one of 2,786 lake-type waterbodies reported to EPA from New Hampshire, and one of 2,233 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 6,774 assessed acres it ranks 473rd 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 472 lakes with a larger one.
Not yet on record
The state has not yet filed a definitive recreation verdict for this record; that field populates when it reports it in a future Integrated Report cycle.
In context
Where Squam Lake 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
6,774 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
5 Longer than most more listed causes than 97% 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 Squam Lake. Hover or tap any bar for its full count and share.
In context
New Hampshire context
ATTAINS carries 2,786 lake-type waterbodies in New Hampshire, 2,783 assessed as not supporting at least one use and 0 fully supporting. Among the 2,233 indexed units there, Squam Lake ranks 35th by listed-cause count (5 listed causes) and 2nd by assessed size among the 2,233 with an area filed; it sits in the not-supporting set (2,783 statewide) . Its listed causes include Mercury - Fish Consumption Advisory, Dissolved Oxygen Saturation, and pH, which also appear among New Hampshire's most-filed impairment causes (led by Mercury - Fish Consumption Advisory). It also lists Dissolved Oxygen and PCBs - Fish Consumption Advisory, outside that top-five list.
| Other large assessed lakes in New Hampshire | Assessed acres |
|---|---|
| Lake Winnipesaukee Not Supporting | 44,315 |
| Lake Umbagog Not Supporting | 4,639 |
| Newfound Lake Not Supporting | 4,440 |
| Lake Winnisquam Not Supporting | 4,203 |
| Sunapee Lake Not Supporting | 4,115 |
| Connecticut River - Gilman Dam Pond Not Supporting | 3,800 |
Peers near Squam Lake's size or cause load
Similar assessed acres
Nearest filed extents (6,774 acres here).
- Twin Buttes Reservoir · 6,772 acres · TX
- Horsehead Lake · 6,778 acres · ND
- Cranberry Lake · 6,795 acres · NY
- Owasco Lake · 6,797 acres · NY
Similar cause load
Nearest listed-cause counts (5 here). Peers already in the acreage column are omitted.
- Alexandria Lake No. 3 · 5 causes · NE
- Alexauken Ck (above 74d 55m) · 5 causes · NJ
- Alexauken Ck (below 74d 55m to 11BA06) · 5 causes · NJ
- Alloway Ck (Quinton to Alloway-WdstwnRd) · 5 causes · NJ
What to do with this record
- The fish-consumption use is assessed as not supporting. Before eating fish from this reservoir, 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 NHLAK700010501-04-01. 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.