Washington reservoir · state assessment record
Lake Sammamish (142 acres)
Assessment decisions reported by Washington to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2022 reporting cycle.
- 142
- Assessed acres
- Lake / Reservoir / Pond
- Water type
This waterbody in one line
Lake Sammamish, a reservoir in Washington, is assessed as not supporting one or more designated uses, with one listed impairment cause in the state's most recent Integrated Report cycle (2022). By assessed acreage it sits in the upper quartile by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (one listed cause vs 23,610 assessed lakes). Aquatic life is assessed as not supporting.
- Not Supporting
- overall status
- P76
- Assessed size nationally
- P20
- Shorter cause list
- Not Supporting
- aquatic life
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.
Where Lake Sammamish stands in the filed 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 Sammamish nationally is assessed size: 142.2 acres, larger than 76% of the 38,628 lake-type units with an area on file.
Every ruled-on use is not supporting
On the uses this filer ruled on, aquatic life, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
Lake Sammamish: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Lake Sammamish. 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 Sammamish 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, Washington carries 832 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Lake Sammamish 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 |
|---|---|---|
| Aquatic Life - Core Summer Salmonid Habitat | Aquatic-life or related | Not Supporting |
The record
Listed impairment causes
Causes the state listed as impairing designated uses of this reservoir, with the cycle each was first listed and the Clean Water Act action recorded against it.
| Cause | Affected uses | First listed | Cleanup standing |
|---|---|---|---|
| pH | Aquatic Life - Core Summer Salmonid Habitat | 2022 | TMDL priority: Low |
Reading the record
Where Lake Sammamish sits among peers
272 of 272 Washington lakes assessed this deeply also had no use supported (every lake judged to this depth, so the outcome does not set this record apart)
Washington ruled definitively on a single designated use at Lake Sammamish and found it not supported. The dataset shows 272 Washington lakes judged to that same depth.
Washington's assessed lakes are most often judged on 1 use, as this one was.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 0 | 0 | 0 | 0 | 0 |
| Mixed | Not possible | 0 | 0 | 0 | 0 |
| None supported | 272 (this record) | 89 | 22 | 8 | 2 |
Ringed cell: Lake Sammamish. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Lake Sammamish is one of 832 lake-type waterbodies reported to EPA from Washington, and one of 385 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 142 assessed acres it ranks 9,228th 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 9,227 lakes with a larger one.
Open in the register
The state has not yet filed a definitive fish-consumption verdict and a definitive recreation verdict for this record; those fields populate when it reports them in a future Integrated Report cycle.
In context
Where Lake Sammamish 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
142 Top 24% larger than 76% 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 Sammamish. Hover or tap any bar for its full count and share.
In context
Washington context
ATTAINS carries 832 lake-type waterbodies in Washington, 393 assessed as not supporting at least one use and 0 fully supporting. Among the 385 indexed units there, Lake Sammamish ranks 216th by listed-cause count (one listed cause) and 154th by assessed size among the 385 with an area filed; it sits in the not-supporting set (393 statewide) . Its listed causes include pH, which also appears among Washington's most-filed impairment causes (led by Non-Native Aquatic Plants).
| Other large assessed lakes in Washington | Assessed acres |
|---|---|
| Bumping Lake Not Assessed | 1,354 |
| Sullivan Lake Not Supporting | 1,298 |
| Deer Lake Not Supporting | 1,146 |
| Loon Lake Not Supporting | 1,094 |
| American Lake Not Supporting | 1,092 |
| Newman Lake Not Supporting | 1,091 |
Peers near Lake Sammamish's size or cause load
Similar assessed acres
Nearest filed extents (142 acres here).
- Bog · 142 acres · MN
- Gust · 142 acres · MN
- Big Boulder Lakes · 142 acres · ID
- Posey Lake · 142 acres · MI
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
- Assessment verdicts are cycle-based, not real-time. For fish-consumption decisions, your state advisory program is the binding source. Consumption status guide
- 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 WA47122F0I8_01_01. 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.