New Hampshire impoundment · state assessment record
Mascoma River - Rivermill
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.
- 20
- Assessed acres
- Impoundment
- Water type
This waterbody in one line
Mascoma River - Rivermill, an impoundment in New Hampshire, is assessed as not supporting one or more designated uses, with 2 listed impairment causes in the state's most recent Integrated Report cycle (2024). By assessed acreage it sits below the national median by assessed acreage (38,628 lakes); its impairment list is among the longest nationally (2 listed causes vs 23,610 assessed lakes). Fish consumption is assessed as not supporting.
- Not Supporting
- overall status
- P32
- Assessed size nationally
- P10
- Shorter cause list
- Not Supporting
- fish consumption
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.
Mascoma River - Rivermill 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: 2 listed impairment causes, a longer list than 80% of assessed lake-type units (n=23,610). List length tracks how states sample and code, not a severity score.
Every ruled-on use is not supporting
On the uses this filer ruled on, fish consumption, recreation, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
Mascoma River - Rivermill: Category 4A reading
Category 4A means a TMDL (or equivalent) is already approved for the impairment on Mascoma River - Rivermill. The remaining work is implementation and tracking, read the cleanup-standing and cause rows for what the state already committed to address.
Overall status: not supporting
The filer's overall status for Mascoma River - Rivermill is Not Supporting. That tile summarizes the assessment unit; the designated-use rows and cause list are the evidence behind it.
Small assessed unit
20 acres puts Mascoma River - Rivermill in the lower tercile by assessed area. Small units are often beaches, ponds, or segments, read the water-type and co-filed notes before comparing them to a multi-thousand-acre reservoir.
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 Mascoma River - Rivermill 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. Monitoring behind at least one of these designated-use verdicts ran through 2023, as New Hampshire filed it. 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 |
|---|---|---|
| Fish Consumption | Fish-consumption or fishery | Not Supporting |
| Potential Drinking Water Supply | Drinking-water supply designation | Fully Supporting |
| Primary Contact Recreation | Recreation | Not Supporting |
| Aquatic Life Integrity | Aquatic-life or related | Insufficient Information |
| Secondary Contact Recreation | Recreation | Insufficient Information |
The record
Listed impairment causes
Causes the state listed as impairing designated uses of this impoundment, 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 |
| Escherichia coli (E. coli) | Primary Contact Recreation Also assessed as meeting: Secondary Contact Recreation | 2004 | Action recorded (type not published) |
Reading the record
Mascoma River - Rivermill: Category 4A reading
4A Category 4A: impaired, TMDL completed
New Hampshire 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
Mascoma River - Rivermill 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 20 assessed acres it ranks 26,138th 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 26,137 lakes with a larger one.
Not yet on record
The state has not yet filed a definitive aquatic-life verdict for this record; that field populates when it reports it in a future Integrated Report cycle.
In context
Where Mascoma River - Rivermill 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
20 Top 68% larger than 32% 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 Mascoma River - Rivermill. 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, Mascoma River - Rivermill ranks 495th by listed-cause count (2 listed causes) and 697th 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 and Escherichia coli (E. coli), which also appear among New Hampshire's most-filed impairment causes (led by Mercury - Fish Consumption Advisory).
| Other large assessed lakes in New Hampshire | Assessed acres |
|---|---|
| Lake Winnipesaukee Not Supporting | 44,315 |
| Squam Lake Not Supporting | 6,774 |
| Lake Umbagog Not Supporting | 4,639 |
| Newfound Lake Not Supporting | 4,440 |
| Lake Winnisquam Not Supporting | 4,203 |
| Sunapee Lake Not Supporting | 4,115 |
Peers near Mascoma River - Rivermill's size or cause load
Similar assessed acres
Nearest filed extents (20 acres here).
- Ada Hayden Heritage Park Lake · 20 acres · IA
- Albany By-Pass Pond · 20 acres · GA
- Alma Lake · 20 acres · IN
- Altamont Old · 20 acres · IL
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 impoundment, 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 NHIMP801060106-02. 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.