State ranking · impaired share of definitive verdicts
States by impaired share of lake assessments
The share of each state's DEFINITIVE lake verdicts (Fully Supporting or Not Supporting) that came back Not Supporting, computed from the Integrated Report decisions state agencies and tribal nations filed with EPA ATTAINS across reporting cycles 1987-2026. A state's figures cover every organization reporting inside its borders, including sovereign tribal nations filing under Clean Water Act section 518. States assess different lakes with different intensity, so this share describes assessment outcomes, not a complete census of state water quality.
- 100%
- Highest share: New Hampshire
- 48.6%
- National average share
- 36
- States above the sample floor
- 100
- Minimum definitive verdicts
This ranking in one line
New Hampshire has the highest impaired share among qualifying states: 100% of its 2,783 definitive verdicts are Not Supporting, well above national average of 48.6%. States with fewer than 100 definitive verdicts are excluded because small samples make shares unstable.
- Highest share
- New Hampshire (100%)
- National average
- 48.6%
- Its definitive verdicts
- 2,783
- Sample floor
- 100 definitive verdicts
It does not lead alone: one other row ties it at 100%, and nothing in the source separates them.
Assessment scale vs. impaired share
A state that assesses more lakes is not thereby a state with a better or worse verdict rate: Wisconsin carries the largest assessed corpus among qualifying states (4,718 definitive verdicts) yet sits at 10.4% impaired, while several states with far smaller corpuses post a higher share. Corpus size and verdict rate move independently.
| Name | Definitive verdicts (assessed corpus) | Impaired share (%) |
|---|---|---|
| New Hampshire | 2,783 | 100% |
| Washington | 393 | 100% |
| New Jersey | 604 | 96.5% |
| Massachusetts | 718 | 94.4% |
| Oregon | 178 | 92.7% |
| California | 224 | 90.2% |
| New York | 642 | 87.7% |
| Illinois | 497 | 87.3% |
| Rhode Island | 140 | 85% |
| Oklahoma | 195 | 78.5% |
| Virginia | 231 | 78.4% |
| South Dakota | 186 | 78% |
| Kansas | 316 | 76.3% |
| Iowa | 203 | 67.5% |
| Florida | 1,003 | 63.4% |
| Nebraska | 352 | 62.2% |
| Indiana | 241 | 60.2% |
| North Carolina | 152 | 59.2% |
| Utah | 134 | 57.5% |
| Missouri | 267 | 56.6% |
| Kentucky | 129 | 55.8% |
| Colorado | 163 | 54.6% |
| Minnesota | 3,364 | 53.4% |
| Arkansas | 117 | 53% |
| Alabama | 273 | 52.4% |
| Georgia | 119 | 39.5% |
| South Carolina | 540 | 39.3% |
| Michigan | 2,339 | 34.5% |
| Connecticut | 139 | 31.7% |
| North Dakota | 176 | 29.5% |
| Texas | 433 | 28.9% |
| Pennsylvania | 516 | 26.2% |
| Vermont | 712 | 21.6% |
| Idaho | 237 | 21.5% |
| Wisconsin | 4,718 | 10.4% |
| Maine | 303 | 10.2% |
The crosshair sits at the median across the 36 qualifying states on each axis, not the range midpoint, so it splits the group evenly. A state's quadrant reflects assessment scale and outcome rate together, not either one alone.
Data updated 2026-08-17
According to the U.S. Environmental Protection Agency's ATTAINS program, 60,590 lake-type waterbodies carry filed assessment records nationwide, and this ranking compares impaired share across the 36 states above the sample floor using the August 2026 extract. See our methodology for denominator rules and refresh cadence.
The assessed universe behind each share
Definitive lake verdicts each top-ranked state filed
- New Hampshire
New Hampshire
2,783 definitive verdicts
- Washington 393
Washington
393 definitive verdicts
- New Jersey 604
New Jersey
604 definitive verdicts
- Massachusetts 718
Massachusetts
718 definitive verdicts
- Oregon 178
Oregon
178 definitive verdicts
- California 224
California
224 definitive verdicts
- New York 642
New York
642 definitive verdicts
- Illinois 497
Illinois
497 definitive verdicts
- Rhode Island 140
Rhode Island
140 definitive verdicts
- Oklahoma 195
Oklahoma
195 definitive verdicts
- Virginia 231
Virginia
231 definitive verdicts
- South Dakota 186
South Dakota
186 definitive verdicts
- Kansas 316
Kansas
316 definitive verdicts
- Iowa 203
Iowa
203 definitive verdicts
- Florida 1,003
Florida
1,003 definitive verdicts
What this shows New Hampshire reached this ranking on 2,783 definitive verdicts and Rhode Island on 140, a 20x difference in sample size behind two shares the ranking prints side by side.
Every row
Full ranking
| # | Name | Impaired share |
|---|---|---|
| 1 | New Hampshire 2,783 | 100% |
| 1 | Washington 393 | 100% |
| 3 | New Jersey 604 | 96.5% |
| 4 | Massachusetts 718 | 94.4% |
| 5 | Oregon 178 | 92.7% |
| 6 | California 224 | 90.2% |
| 7 | New York 642 | 87.7% |
| 8 | Illinois 497 | 87.3% |
| 9 | Rhode Island 140 | 85% |
| 10 | Oklahoma 195 | 78.5% |
| 11 | Virginia 231 | 78.4% |
| 12 | South Dakota 186 | 78% |
| 13 | Kansas 316 | 76.3% |
| 14 | Iowa 203 | 67.5% |
| 15 | Florida 1,003 | 63.4% |
| 16 | Nebraska 352 | 62.2% |
| 17 | Indiana 241 | 60.2% |
| 18 | North Carolina 152 | 59.2% |
| 19 | Utah 134 | 57.5% |
| 20 | Missouri 267 | 56.6% |
| 21 | Kentucky 129 | 55.8% |
| 22 | Colorado 163 | 54.6% |
| 23 | Minnesota 3,364 | 53.4% |
| 24 | Arkansas 117 | 53% |
| 25 | Alabama 273 | 52.4% |
| 26 | Georgia 119 | 39.5% |
| 27 | South Carolina 540 | 39.3% |
| 28 | Michigan 2,339 | 34.5% |
| 29 | Connecticut 139 | 31.7% |
| 30 | North Dakota 176 | 29.5% |
| 31 | Texas 433 | 28.9% |
| 32 | Pennsylvania 516 | 26.2% |
| 33 | Vermont 712 | 21.6% |
| 34 | Idaho 237 | 21.5% |
| 35 | Wisconsin 4,718 | 10.4% |
| 36 | Maine 303 | 10.2% |
2 of the 36 rows in this table tie on the ranked value: 2 at 100% (rank 1). 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.
Share = Not Supporting / (Not Supporting + Fully Supporting) per state, over lake-type waterbodies only. The share is Not Supporting divided by definitive lake verdicts (Fully Supporting or Not Supporting) that rule on at least one of the four designated uses this site reports: lake waterbodies without a definitive verdict are excluded from both the numerator and the denominator. Verdicts recorded as Fully Supporting without a ruling on any of those four uses are excluded: some states file a placeholder unit for the lakes they have not assessed and report it as supporting on uses like irrigation and navigation, which would read as clean water in a comparison between states. States with fewer than 100 definitive verdicts are excluded because small samples make shares unstable.
Reading this ranking
- A high share can mean worse water, targeted monitoring, or stricter standards; the state page shows the underlying mix. States hub
- Assessment coverage differs sharply by state; raw reported counts are on the states hub. How assessment works
- See which causes drive listings nationally. Most-listed lakes
Rankings order reported source data; they are not endorsements or safety determinations.
Rankings are computed from state assessment decisions in EPA's ATTAINS system and USGS National Water Information System daily values; the ordering metric and any exclusion floor are stated above the table, no number is typed in by an editor. Computed from per-state rollups of the full ingested ATTAINS lake-type universe; the sample floor and denominator definition are stated in the method note. 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.