State water-quality picture · #4 by reported lake-type waterbodies
New Hampshire lakes and reservoirs
Every figure on this page is computed from the assessment decisions New Hampshire reported to the U.S. Environmental Protection Agency under Clean Water Act sections 303(d) and 305(b) (reporting cycles 2024), plus daily water-level observations from the U.S. Geological Survey.
- 2,786
- Reported waterbodies
- 2,783
- Not supporting a use
- 2,783
- Fish use not supporting
- 0
- Gauged lakes
New Hampshire in one line
2,786 lake-type waterbodies in New Hampshire are reported to EPA ATTAINS across reporting cycles 2024: 2,783 assessed as not supporting at least one designated use, 0 fully supporting, and 3 without a definitive overall verdict. The most-listed impairment cause is Mercury - Fish Consumption Advisory, on 2,783 waterbodies. This ranks the cause names filed in New Hampshire, not distinct pollutants: mercury appears under 2 of them, together listed on 2,785 waterbodies.
- 2,786
- reported waterbodies
- 2,783
- not supporting a use
- 0
- fully supporting
- 100%
- of definitive verdicts impaired
An unassessed waterbody is neither confirmed clean nor confirmed impaired; states assess on multi-year cycles.
New Hampshire's large register still carries a heavy not-supporting share
Among the largest third of state lake-type registers (2,786 units), New Hampshire also sits in the upper third for ruled not-supporting share (100%). The size and the load move together here, not every large inventory does.
Data updated 2026-08-17
According to the U.S. Environmental Protection Agency's ATTAINS program, New Hampshire reported 2,786 lake-type waterbodies in New Hampshire in the August 2026 extract. See our methodology for filer attribution and multi-year reporting cycles.
How New Hampshire's large inventory splits across overall status
Each of the 2,786 lake-type units reported by New Hampshire lands in exactly one overall-status bucket. On a register this large, the bar is an inventory partition, the cause chart and national gauge below answer different questions.
Most-listed impairment causes in New Hampshire
Waterbodies carrying each listed cause, most first
- Mercury - Fish Consumption Advisory
Mercury - Fish Consumption Advisory
2,783 waterbodies
- pH 483
pH
483 waterbodies
- Escherichia coli (E. coli) 125
Escherichia coli (E. coli)
125 waterbodies
- Cyanobacteria Hepatotoxic Microcystins 100
Cyanobacteria Hepatotoxic Microcystins
100 waterbodies
- Dissolved Oxygen Saturation 99
Dissolved Oxygen Saturation
99 waterbodies
What this shows Mercury - Fish Consumption Advisory is the most-listed impairment cause in New Hampshire, on 2,783 of the lake-type waterbodies reported there. This ranks the cause names filed in New Hampshire, not distinct pollutants: mercury appears under 2 of them, together listed on 2,785 waterbodies.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
New Hampshire: 100% of ruled verdicts are not-supporting, against a national share of 53%, 1.9× the national rate.
Reporting practice
A definitive verdict covers nearly all of New Hampshire's inventory
Each reporting authority decides how much of the water it files to EPA it actually assesses in a cycle. That decision sets the denominator behind every count on this page.
New Hampshire holds the 4th-largest reported lake-type inventory in the country, 2,786 assessment units, carrying a definitive verdict on 99.9% of it. The counts above describe the 2,783 units carrying a verdict, not all 2,786 reported. New Hampshire has also retired 24 lake-type assessment units, superseded filings that are kept on the site but not counted here.
The states reporting at the nearest rates are Vermont (100%) and New Jersey (98.9%).
Assessing more of an inventory is a reporting choice, set by cycle length, monitoring budget and how finely a state splits its waters into units. It is not a measure of water quality, and it is why a raw count from one state does not sit beside a raw count from another. How assessment coverage varies.
New Hampshire against every comparable state
Share of reported lake-type waterbodies carrying a definitive verdict
99.9% 3rd of 47 higher than 44 of 47 states
the 47 comparable states, by definitive-verdict share
Each bar is a band; taller bars hold more states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA ATTAINS · Reporting cycles 1987–2026
Each bar counts states whose definitive-verdict share falls in that 10-point band. The 47 states shown are those reporting at least 25 lake-type units; a share off a smaller inventory is precision the data does not have.
By size
Largest assessed lakes in New Hampshire
By assessed acreage as reported in ATTAINS. Acreage is the assessed unit's size, which can differ from a lake's full surface area.
| # | Waterbody | Assessed acres |
|---|---|---|
| 1 | Lake Winnipesaukee Not Supporting | 44,315 |
| 2 | Squam Lake Not Supporting | 6,774 |
| 3 | Lake Umbagog Not Supporting | 4,639 |
| 4 | Newfound Lake Not Supporting | 4,440 |
| 5 | Lake Winnisquam Not Supporting | 4,203 |
| 6 | Sunapee Lake Not Supporting | 4,115 |
| 7 | Connecticut River - Gilman Dam Pond Not Supporting | 3,800 |
| 8 | Ossipee Lake Not Supporting | 3,242 |
| 9 | Lake Wentworth Not Supporting | 3,089 |
| 10 | First Connecticut Lake Not Supporting | 3,063 |
| 11 | Massabesic Lake Not Supporting | 2,554 |
| 12 | Connecticut River - Vernon Dam Not Supporting | 2,000 |
By cause count
Most-listed waterbodies in New Hampshire
Waterbodies carrying the most listed impairment causes among the lake-type units reported by New Hampshire.
| # | Waterbody | Listed causes |
|---|---|---|
| 1 | Taylor River Refuge Pond Not Supporting | 16 |
| 2 | Rice Dam Pond - on Taylor River Not Supporting | 10 |
| 3 | Ashuelot River - Fisk Mill Hydro Not Supporting | 8 |
| 3 | Robinson Pond Not Supporting | 8 |
| 3 | Webster Stream - Locke Lake Not Supporting | 8 |
| 6 | Adder Pond Not Supporting | 7 |
| 6 | Captain Pond Not Supporting | 7 |
| 6 | Hunkins Pond Not Supporting | 7 |
| 6 | Nutt Pond Not Supporting | 7 |
| 6 | Pawtuckaway Lake Not Supporting | 7 |
8 of the 10 rows in this table tie on the ranked value: 3 at 8 (rank 3), 5 at 7 (rank 6). Tied rows share a rank and are listed in no meaningful order; where a tie reaches the top the medal is shared, because nothing separates those rows.
States near New Hampshire's heavier not-supporting load
Two EPA ATTAINS peer sets outside New Hampshire. The reporting-practice chart above stays on definitive-verdict share; the neighborhoods below emphasize cross-state nearest neighbors when the not-supporting count is in the upper third.
Similar reported inventory
Nearest states by lake-type units on the register (2,786 here).
Comparable not-supporting counts
Nearest states by units assessed not supporting a use (2,783 here). Inventory peers above are omitted.
- Minnesota · 1,798 not supporting · 985 off
- Michigan · 807 not supporting · 1,976 off
- Massachusetts · 678 not supporting · 2,105 off
- New Jersey · 583 not supporting · 2,200 off
Peers are nearest-neighbor matches on EPA ATTAINS register size and not-supporting counts among states with at least 25 reported units. Impairment peers skip states already listed in the inventory column so the two link sets stay distinct.
Using this state picture
- Comparisons across states hold on shares, not counts: 99.9% of the inventory reported from New Hampshire carries a definitive verdict, 3rd of 47 comparable states. National rankings
- Fish-consumption verdicts here are assessment decisions. Species-level meal advice comes from the state fish-advisory program. Consumption guide
- Browse every named New Hampshire waterbody with a populated record. Browse waterbodies
PlainLakes renders state assessment decisions and federal gauge observations without modification.
Figures on this page are computed from the assessment decisions New Hampshire reported to EPA's ATTAINS system and from USGS National Water Information System daily values, no number is typed in by an editor. State counts aggregate every lake-type assessment unit reported by New Hampshire, including unnamed units that never receive their own page. 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.