Arizona lake · state assessment record
Lake Powell
Assessment decisions reported by Arizona to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2026 reporting cycle.
- 9,770
- Assessed acres
- Lake, Freshwater
- Water type
- 3,522.7 ft
- Water Surface Elevation (provisional)
This waterbody in one line
Lake Powell, a lake in Arizona, is assessed as not supporting one or more designated uses, with one listed impairment cause in the state's most recent Integrated Report cycle (2026). 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 (one listed cause vs 23,610 assessed lakes). Fish consumption is assessed as not supporting. A USGS gauge tracks its water surface elevation daily.
- Not Supporting
- overall status
- P99
- Assessed size nationally
- P20
- 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.
Lake Powell 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 Lake Powell nationally is assessed size: 9,770 acres, larger than 99% of the 38,628 lake-type units with an area on file.
Every filed use falls short
On the uses this filer ruled on, fish consumption, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
Lake Powell: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Lake Powell. 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 Lake Powell is Not Supporting. That tile summarizes the assessment unit; the designated-use rows and cause list are the evidence behind it.
Typical cause-list length
1 listed cause is a middle-tercile list length among assessed lake-type units. Look to IR category and use outcomes for the distinctive reading.
According to the U.S. Environmental Protection Agency's ATTAINS program, Arizona carries 78 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Lake Powell 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.
| Designated use | Group | Verdict |
|---|---|---|
| Agricultural Irrigation | Other | Fully Supporting |
| Agricultural Livestock Watering | Other | Fully Supporting |
| Fish Consumption | Fish-consumption or fishery | Not Supporting |
| Aquatic and Wildlife (Coldwater Fishery) | Aquatic-life or related | Insufficient Information |
| Domestic Water Source | Drinking-water supply designation | Insufficient Information |
| Full Body Contact | Recreation | Insufficient Information |
The record
Listed impairment causes
Causes the state listed as impairing designated uses of this lake, with the cycle each was first listed and the Clean Water Act action recorded against it.
| Cause | Affected uses | First listed | Cleanup standing |
|---|---|---|---|
| Mercury in Fish Tissue | Fish Consumption | 2022 | TMDL priority: High |
Reading the record
Cleanup queue for Lake Powell
1 listed cause ranked High in the TMDL queue, still without a plan
Arizona ranked Mercury in Fish Tissue high in its TMDL development queue, and no cleanup plan is on file for that listing yet. That queue rank is the state's own scheduling signal, not an EPA national rule.
A High ranking names a position in the state's plan-writing queue; it is not a measure of how impaired the water is. How listing and cleanup work.
Scale and rank
Lake Powell is one of 78 lake-type waterbodies reported to EPA from Arizona, and one of 44 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 9,770 assessed acres it ranks 336th 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 335 lakes with a larger one.
Water level
A USGS gauge tracks this lake's water surface elevation daily, and the latest reading is 3.80 ft below the reading 30 days earlier, against a 365-day observed range of 31.6 ft. The state has not yet filed a definitive recreation verdict and a definitive aquatic-life verdict for this record; those fields populate when it reports them in a future Integrated Report cycle.
Reported trophic class
Arizona carried the trophic field for this assessment unit and filed it as unclassified, which records that no class was determined rather than that the water is unenriched. What the trophic scale measures.
Water level: 365-day record
Daily water surface elevation values, feet above the North American Vertical Datum of 1988 (NAVD 88), from USGS gauge 09379900 (Lake Powell at Glen Canyon Dam, Az), shown weekly. Readings are daily-batch snapshots, not real-time conditions.
- Latest reading
- 3,522.7 ft 3.800000000000182ft vs 30 days earlier
- 2026-08-15 · Provisional, subject to USGS revision
Water level: 365-day record
Subscribe to water level updates for Lake Powell (RSS)
60 of the 365 daily values in this window (16%) are provisional and subject to USGS revision; USGS has approved this gauge's record through 2026-06-16.
Full gauge record: USGS monitoring location 09379900
In context
Where Lake Powell 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
9,770 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
1 Longer than most more listed causes than 49% 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 Lake Powell. Hover or tap any bar for its full count and share.
In context
Arizona context
ATTAINS carries 78 lake-type waterbodies in Arizona, 34 assessed as not supporting at least one use and 20 fully supporting. Among the 44 indexed units there, Lake Powell ranks 14th by listed-cause count (one listed cause) and 4th by assessed size among the 44 with an area filed; it sits in the not-supporting set (34 statewide) . Its listed causes include Mercury in Fish Tissue, which also appears among Arizona's most-filed impairment causes (led by Mercury in Fish Tissue).
| Other large assessed lakes in Arizona | Assessed acres |
|---|---|
| Lake Mohave Not Supporting | 27,044 |
| Lake Havasu Not Supporting | 19,780 |
| Roosevelt Lake Not Supporting | 18,345 |
| Lake Pleasant Not Supporting | 8,000 |
| Topock Marsh Not Assessed | 4,870 |
| Bartlett Lake Not Supporting | 2,376 |
Peers near Lake Powell's size or cause load
Similar assessed acres
Nearest filed extents (9,770 acres here).
- Lake Tawakoni · 9,766 acres · TX
- Lake Mendota · 9,781 acres · WI
- Lake Poinsett · 9,795 acres · SD
- Chattahoochee River (Walter F. George Lake) · 9,797 acres · AL
Similar cause load
Nearest listed-cause counts (1 here). Peers already in the acreage column are omitted.
- Aaron · 1 causes · MN
- Aaron River Reservoir · 1 causes · MA
- Abbotts Creek (including Lexington-Thomasville Water Supply Reservoir at normal reservoir elevation, Tom-A-Lex Lake) · 1 causes · NC
- Abeniki Lake · 1 causes · NH
What to do with this record
- The fish-consumption use is assessed as not supporting. Before eating fish from this lake, check your state fish-advisory program for species-specific meal limits. Consumption status guide
- Water levels shown are daily snapshots. Seasonal drawdown and datum conventions matter when comparing levels. How to read level data
- 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 AZL14070006-1130_00. 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.