State water-quality picture · #41 by reported lake-type waterbodies
Arizona lakes and reservoirs
Every figure on this page is computed from the assessment decisions Arizona reported to the U.S. Environmental Protection Agency under Clean Water Act sections 303(d) and 305(b) (reporting cycles 2006–2026), plus daily water-level observations from the U.S. Geological Survey.
- 78
- Reported waterbodies
- 34
- Not supporting a use
- 23
- Fish use not supporting
- 2
- Gauged lakes
Arizona in one line
78 lake-type waterbodies in Arizona are reported to EPA ATTAINS across reporting cycles 2006–2026: 34 assessed as not supporting at least one designated use, 20 fully supporting, and 24 without a definitive overall verdict. The most-listed impairment cause is Mercury in Fish Tissue, on 23 waterbodies. This ranks the cause names filed in Arizona, not distinct pollutants: mercury appears under 2 of them, together listed on 23 waterbodies.
- 78
- reported waterbodies
- 34
- not supporting a use
- 20
- fully supporting
- 64%
- of definitive verdicts impaired
An unassessed waterbody is neither confirmed clean nor confirmed impaired; states assess on multi-year cycles. 1 of those 20 fully supporting verdicts (5%) rest on designated uses this site does not report (irrigation, navigation and industrial water supply), with Arizona recording no verdict on fish consumption, recreation, aquatic life and drinking water. They are counted above because the state filed them, and excluded from the impaired share below because that figure compares states.
Arizona's smaller reported lake-type inventory
At 78 units, Arizona is in the lowest third of state lake-type registers. The charts below describe that compact filing set, not a national-scale inventory.
Data updated 2026-08-17
According to the U.S. Environmental Protection Agency's ATTAINS program, Arizona reported 78 lake-type waterbodies in Arizona in the August 2026 extract. See our methodology for filer attribution and multi-year reporting cycles.
Overall-status split on Arizona's compact register
Every reported lake-type unit in this smaller Arizona filing set falls into exactly one overall-status bucket. The bar partitions 78 units; cause and gauge panels below stay separate.
Most-listed impairment causes in Arizona
Waterbodies carrying each listed cause, most first
- Mercury in Fish Tissue
Mercury in Fish Tissue
23 waterbodies
- Dissolved Oxygen 8
Dissolved Oxygen
8 waterbodies
- pH 7
pH
7 waterbodies
- Ammonia-Nitrogen 2
Ammonia-Nitrogen
2 waterbodies
- Nitrogen, Total 2
Nitrogen, Total
2 waterbodies
What this shows Mercury in Fish Tissue is the most-listed impairment cause in Arizona, on 23 of the lake-type waterbodies reported there. This ranks the cause names filed in Arizona, not distinct pollutants: mercury appears under 2 of them, together listed on 23 waterbodies.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
Arizona: 64% of ruled verdicts are not-supporting, against a national share of 53%, 1.2× the national rate.
Reporting practice
Where Arizona stands on definitive-verdict coverage
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.
Arizona holds the 41st-largest reported lake-type inventory in the country, 78 assessment units, carrying a definitive verdict on 67.9% of it. The counts above describe the 53 units carrying a verdict, not all 78 reported. Arizona has also retired 2 lake-type assessment units, superseded filings that are kept on the site but not counted here.
The states reporting at the nearest rates are Florida (68%) and Tennessee (65%).
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.
Arizona against every comparable state
Share of reported lake-type waterbodies carrying a definitive verdict
67.9% 24th of 47 higher than 23 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 Arizona
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 Mohave Not Supporting | 27,044 |
| 2 | Lake Havasu Not Supporting | 19,780 |
| 3 | Roosevelt Lake Not Supporting | 18,345 |
| 4 | Lake Powell Not Supporting | 9,770 |
| 5 | Lake Pleasant Not Supporting | 8,000 |
| 6 | Topock Marsh Not Assessed | 4,870 |
| 7 | Bartlett Lake Not Supporting | 2,376 |
| 8 | Apache Lake Not Supporting | 2,192 |
| 9 | Alamo Lake Not Supporting | 1,415 |
| 10 | Lyman Reservoir Not Supporting | 1,308 |
| 11 | Saguaro Lake Fully Supporting | 1,022 |
| 12 | Lake Mary (Upper) Not Supporting | 861 |
By cause count
Most-listed waterbodies in Arizona
Waterbodies carrying the most listed impairment causes among the lake-type units reported by Arizona.
| # | Waterbody | Listed causes |
|---|---|---|
| 1 | Luna Lake Not Supporting | 4 |
| 2 | Alamo Lake Not Supporting | 3 |
| 2 | Lakeside Lake Not Supporting | 3 |
| 2 | Rainbow Lake Not Supporting | 3 |
| 2 | Watson Lake Not Supporting | 3 |
| 6 | Apache Lake Not Supporting | 2 |
| 6 | Canyon Lake Not Supporting | 2 |
| 6 | Peck's Lake Not Supporting | 2 |
| 6 | Pena Blanca Lake Not Supporting | 2 |
| 6 | Stoneman Lake Not Supporting | 2 |
9 of the 10 rows in this table tie on the ranked value: 4 at 3 (rank 2), 5 at 2 (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.
Gauge network
Lakes with a daily level record in Arizona
Lakes with a linked USGS gauge and a daily water-level record. Readings are daily-batch snapshots, not real-time.
States with similar inventory scale or impairment load
Two EPA ATTAINS peer sets outside Arizona. The reporting-practice chart above stays on definitive-verdict share; these neighborhoods are cross-state nearest neighbors on register size and not-supporting counts.
States with a similar reported inventory
Nearest states by lake-type units on the register (78 here).
Similar not-supporting load
Nearest states by units assessed not supporting a use (34 here). Inventory peers above are omitted.
- Maryland · 32 not supporting · 2 off
- Maine · 31 not supporting · 3 off
- Delaware · 40 not supporting · 6 off
- Connecticut · 44 not supporting · 10 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: 67.9% of the inventory reported from Arizona carries a definitive verdict, 24th 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 Arizona 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 Arizona 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 Arizona, 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.