Some of these decisions are EPA's. 8 of these 832 records carry a Clean Water Act cleanup plan EPA established rather than Washington. They are counted in every figure on this page, and each record page names which.
State water-quality picture · #10 by reported lake-type waterbodies
Washington lakes and reservoirs
Every figure on this page is computed from the assessment decisions Washington reported to the U.S. Environmental Protection Agency under Clean Water Act sections 303(d) and 305(b) (reporting cycles 2010–2022), plus daily water-level observations from the U.S. Geological Survey.
- 832
- Reported waterbodies
- 393
- Not supporting a use
- 126
- Fish use not supporting
- 1
- Gauged lake
Washington in one line
832 lake-type waterbodies in Washington are reported to EPA ATTAINS across reporting cycles 2010–2022: 393 assessed as not supporting at least one designated use, 0 fully supporting, and 439 without a definitive overall verdict. The most-listed impairment cause is Non-Native Aquatic Plants, on 168 waterbodies.
- 832
- reported waterbodies
- 393
- 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.
Washington's large register still carries a heavy not-supporting share
Among the largest third of state lake-type registers (832 units), Washington 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, Washington reported 832 lake-type waterbodies in Washington in the August 2026 extract. See our methodology for filer attribution and multi-year reporting cycles.
How Washington's large inventory splits across overall status
Each of the 832 lake-type units reported by Washington 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 Washington
Waterbodies carrying each listed cause, most first
- Non-Native Aquatic Plants
Non-Native Aquatic Plants
168 waterbodies
- Phosphorus, Total
Phosphorus, Total
84 waterbodies
- PCBs in Fish Tissue 62
PCBs in Fish Tissue
62 waterbodies
- Methylmercury in Fish Tissue 59
Methylmercury in Fish Tissue
59 waterbodies
- pH 45
pH
45 waterbodies
What this shows Non-Native Aquatic Plants is the most-listed impairment cause in Washington, on 168 of the lake-type waterbodies reported there.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
Washington: 100% of ruled verdicts are not-supporting, against a national share of 53%, 1.9× the national rate.
Reporting practice
Where Washington 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.
Washington holds the 10th-largest reported lake-type inventory in the country, 832 assessment units, carrying a definitive verdict on 47.2% of it. The counts above describe the 393 units carrying a verdict, not all 832 reported. Washington has also retired 490 lake-type assessment units, superseded filings that are kept on the site but not counted here.
The states reporting at the nearest rates are Colorado (47.4%) and Missouri (42.9%).
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.
Washington against every comparable state
Share of reported lake-type waterbodies carrying a definitive verdict
47.2% 35th of 47 higher than 12 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 Washington
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 | Bumping Lake Not Assessed | 1,354 |
| 2 | Sullivan Lake Not Supporting | 1,298 |
| 3 | Deer Lake Not Supporting | 1,146 |
| 4 | Loon Lake Not Supporting | 1,094 |
| 5 | American Lake Not Supporting | 1,092 |
| 6 | Newman Lake Not Supporting | 1,091 |
| 7 | Stevens Lake Not Supporting | 1,003 |
| 8 | Wynoochee Lake Not Assessed | 990 |
| 9 | Mason Lake Not Supporting | 977 |
| 10 | Billy Clapp Lake Not Supporting | 973 |
| 11 | Curlew Lake Not Supporting | 861 |
| 12 | Soap Lake Not Assessed | 844 |
By cause count
Most-listed waterbodies in Washington
Waterbodies carrying the most listed impairment causes among the lake-type units reported by Washington.
| # | Waterbody | Listed causes |
|---|---|---|
| 1 | Lake Union / Lake Washington Ship Canal Assessment unit WA47122G3C3_NW Not Supporting | 12 |
| 2 | Lake Union Not Supporting | 11 |
| 3 | Lake Union / Lake Washington Ship Canal Assessment unit WA47122G3E2_NW Not Supporting | 10 |
| 4 | Goose, Upper Lake Not Supporting | 9 |
| 4 | Lake Meridian Not Supporting | 9 |
| 4 | Union Lake / Lake Washington Ship Canal Not Supporting | 9 |
| 7 | Green Lake Not Supporting | 8 |
| 7 | Lake Washington Assessment unit WA47122F2D0_SE Not Supporting | 8 |
| 7 | Lake Washington Assessment unit WA47122F2D0_NE Not Supporting | 8 |
| 10 | Lake Washington Assessment unit WA47122G2D5_01_01 Not Supporting | 7 |
6 of the 10 rows in this table tie on the ranked value: 3 at 9 (rank 4), 3 at 8 (rank 7). Tied rows share a rank and are listed in no meaningful order.
Gauge network
Lakes with a daily level record in Washington
Lakes with a linked USGS gauge and a daily water-level record. Readings are daily-batch snapshots, not real-time.
States near Washington's heavier not-supporting load
Two EPA ATTAINS peer sets outside Washington. 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.
States with a similar reported inventory
Nearest states by lake-type units on the register (832 here).
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: 47.2% of the inventory reported from Washington carries a definitive verdict, 35th 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 Washington 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 Washington 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 Washington, 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.