Computed rankings · stated methods and floors

Lake rankings

Every ranking states its ordering metric, source, and any exclusion floor, and links each entry to its full record. Ordering data comes from two federal systems: EPA ATTAINS Integrated Report decisions (Clean Water Act sections 303(d) and 305(b), reporting cycles 1987-2026) and USGS National Water Information System daily values. Rankings order reported data; they are not endorsements or safety determinations.

Compiled by PlainLakes

8
Rankings: 25–50
Entries per list, at most

Data updated 2026-08-17

What the rankings are drawn from

Across the 24,429 lake-type waterbodies carrying a definitive verdict in the latest reported cycle, 52.5% are assessed as not supporting at least one designated use.

60,590
reported waterbodies: 24,429
definitive verdicts: 78%
of fish-use assessments impaired: 121
with a daily level record

A definitive verdict is Fully Supporting or Not Supporting. Not Assessed and Insufficient Information are excluded from every share on this page.

Largest lakes in the U.S.

Lake-type waterbodies by assessed acreage in ATTAINS.

#1 Superior, MN (13,182,720 acres)

Largest lakes in Michigan

Michigan lake-type units by assessed acreage in ATTAINS.

#1 Lake Huron (Michigan Jurisdiction) (5,815,360 acres)

Most listed impairment causes

Waterbodies carrying the longest state cause lists.

#1 Depue, IL (17 causes)

Largest fully supporting lakes

The biggest lakes whose latest assessment met all evaluated uses.

#1 Gilbert Bay, UT (559,424 acres)

Not Supporting share of definitive verdicts, 100-verdict floor.

#1 New Hampshire (100%)

Biggest 30-day level drops

Lakes with a daily level record, by largest elevation decline.

#1 Paonia Reservoir., CO (-36.88 ft over 30 days)

Biggest 32-day level rises

Lakes with a daily level record, by largest elevation gain.

#1 Schoharie Reservoir, NY (+13.48 ft over 32 days)

Largest reservoirs by storage

Reservoirs carrying a daily USGS storage record, largest first.

#1 Lake Mohave, AZ (1,692,000 acre-ft)

NH

100
WA

100
NJ

97
MA

94
OR

93
CA

90
NY

88
IL

87
RI

85
OK

79
VA

78
SD

78

What this shows Only the 36 states with at least 100 definitive verdicts qualify for this share ranking; small denominators swing a percentage too far to compare fairly. Across those states the share spans 89.8 percentage points, so where a lake sits matters as much as the lake itself. A high share reflects both water quality and how aggressively a state assesses and lists, the two cannot be separated from this data alone.

Depue

17
Taylor River Refuge Pond

16
Devil's Swamp Lake and Bayou Baton Rouge

13
Morses Creek / Piles Creek

13
Passaic R Lwr (Saddle R to Dundee Dam)

13
Lake Union / Lake Washington Ship Canal

12
Salton Sea

11
Cooper River (Rt 130 to Wallworth gage)

11
Hackensack R (Amtrak bridge to Rt 3)

11
Lake Union

11

What this shows A long cause list signals a well-studied waterbody as much as a troubled one, a lake nobody samples cannot accumulate listings. Read the count alongside the state's overall assessment coverage rather than as a standalone severity score.

How these rankings are computed

Every list on this page is ordered by a single stated metric taken directly from a published federal record. Nothing here is scored, weighted, or blended: an ordering that mixes several measures into one index hides which measure actually moved a waterbody up the list, so this site does not publish one.

Size rankings use the assessed size a state reports to EPA, in acres, and include only waterbodies whose reported unit is acres. Reported size is the extent of the assessment unit the state defined, which is not always the whole lake, a large lake split into several units appears as several entries rather than one.

Status rankings use the overall assessment verdict from the state's most recent Integrated Report cycle. Because states assess on multi-year rotations, two lakes on the same list can carry verdicts from different years; each entry's own page states the cycle its verdict came from. An unassessed lake is neither confirmed clean nor confirmed impaired, and never appears in a share calculation.

Water-level rankings use USGS daily values and compare the most recent reading against the reading roughly 30 days earlier for the same gauge and parameter. Only waterbodies this site could conservatively match to a gauge appear, and only where that gauge reports a level in feet - so the movers lists cover 110 assessed lakes, not every lake in the country. The wider 121 carrying a daily USGS water-level record includes reservoirs that report storage in acre-feet, a volume rather than a level, which cannot enter a ranking measured in feet. Levels are daily snapshots pulled by a scheduled job; they are not real-time readings, and they are not flood or safety guidance.

Lists are cut at different depths because the pools behind them differ in size by orders of magnitude: 3 lists stop at 50, 4 lists stop at 25, and one list is not capped at all because its population is small enough to publish whole. Every list states how many rows it published, and says so when more rows qualified than it shows.

Where a ranking could be destabilised by a tiny denominator, it carries an explicit floor rather than a silent filter. The state impaired-share list requires at least 100 definitive verdicts; states below that floor are listed on their own state pages but excluded here, because a state with nine assessed lakes can show 100% impairment without that number meaning what it appears to mean.

Reading these lists honestly

Ranking position reflects reported data, not risk. A lake near the top of an impairment list may simply be the most thoroughly studied one in its state. Methodology
Assessment cycles differ by state, so compare within a state before comparing across states. Browse by state
For fish-consumption decisions, the state advisory is the authority, an assessment verdict is not an advisory. Consumption status guide

Rankings order reported data. They are not endorsements, safety determinations, or a substitute for a state advisory.

According to the U.S. Environmental Protection Agency's ATTAINS program, state agencies and tribal nations report 60,590 lake-type waterbodies nationwide in the August 2026 extract, and PlainLakes renders those filed assessment decisions alongside linked U.S. Geological Survey daily gauge records where a conservative name match exists. See our methodology for reporting-unit limits, filer attribution, and refresh cadence.

Rankings are computed from state assessment decisions in EPA's ATTAINS system and USGS National Water Information System daily values, no number is typed in by an editor. 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.