California reservoir · state assessment record
Schwan Lake
Assessment decisions reported by California to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2020 reporting cycle.
- 23
- Assessed acres
- Lake / Reservoir / Pond
- Water type
This waterbody in one line
Schwan Lake, a reservoir in California, is assessed as not supporting one or more designated uses, with 4 listed impairment causes in the state's most recent Integrated Report cycle (2020). By assessed acreage it sits below the national median by assessed acreage (38,628 lakes); its impairment list is among the longest nationally (4 listed causes vs 23,610 assessed lakes). Aquatic life is assessed as not supporting. California assesses shellfish harvesting as not supported; it reported no verdict on fish consumption itself.
- Not Supporting
- overall status
- P36
- Assessed size nationally
- P3
- 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.
Reading Schwan Lake's filed record
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: cause-list length
The standout filed fact is cause-list length: 4 listed impairment causes, a longer list than 95% of assessed lake-type units (n=23,610). List length tracks how states sample and code, not a severity score.
Every filed use falls short
On the uses this filer ruled on, fish consumption, recreation, aquatic life, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
Schwan Lake: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Schwan Lake. 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 Schwan Lake is Not Supporting. That tile summarizes the assessment unit; the designated-use rows and cause list are the evidence behind it.
Small within California
State size rank 172 of 195 puts Schwan Lake toward the small end of California's indexed lake-type units with an area.
According to the U.S. Environmental Protection Agency's ATTAINS program, California carries 607 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Schwan Lake 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 |
|---|---|---|
| Non-Contact Water Recreation | Recreation | Fully Supporting |
| Shellfish Harvesting | Fish-consumption or fishery | Not Supporting |
| Warm Freshwater Habitat | Aquatic-life or related | Not Supporting |
| Water Contact Recreation | Recreation | 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 |
|---|---|---|---|
| Escherichia coli (E. coli) | Water Contact Recreation Also assessed as meeting: Non-Contact Water Recreation | 2018 | None reported |
| Fecal Coliform | Water Contact Recreation Also assessed as meeting: Non-Contact Water Recreation | 2018 | None reported |
| Nutrients | Warm Freshwater Habitat | 2018 | None reported |
| Total Coliform | Shellfish Harvesting | 2018 | None reported |
Probable sources
California listed the source of the impairment as unknown. That is the state's own filed value, not a gap in this record: the cause has been identified, the origin has not.
Reading the record
Where Schwan Lake sits among peers
8 of 15 California lakes assessed this deeply also came out mixed
California ruled definitively on 4 designated uses at Schwan Lake and found 3 of 4 not supported. The dataset shows 15 California lakes judged to that same depth.
California's assessed lakes are most often judged on 2 uses; this one was judged on 4.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 11 | 8 | 0 | 0 | 3 |
| Mixed | Not possible | 3 | 10 | 8 (this record) | 8 |
| None supported | 46 | 107 | 11 | 7 | 2 |
Ringed cell: Schwan Lake. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Schwan Lake is one of 607 lake-type waterbodies reported to EPA from California, and one of 195 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 23 assessed acres it ranks 24,775th 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 24,774 lakes with a larger one.
In context
Where Schwan Lake 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
23 Top 64% larger than 36% 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
4 Longer than most more listed causes than 95% 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 Schwan Lake. Hover or tap any bar for its full count and share.
In context
California context
ATTAINS carries 607 lake-type waterbodies in California, 202 assessed as not supporting at least one use and 22 fully supporting. Among the 195 indexed units there, Schwan Lake ranks 25th by listed-cause count (4 listed causes) and 172nd by assessed size among the 195 with an area filed; it sits in the not-supporting set (202 statewide) . Its listed causes (Escherichia coli (E. coli), Fecal Coliform, Nutrients, and Total Coliform) sit outside California's top-five list, which is led by Mercury.
| Other large assessed lakes in California | Assessed acres |
|---|---|
| Salton Sea Not Supporting | 233,045 |
| Tahoe, Lake Not Supporting | 84,092 |
| Goose Lake (Modoc County) Not reported | 62,385 |
| Honey Lake Not Supporting | 55,526 |
| Klamath River HU, Tule Lake and Lower Klamath Lake National Wildlife Refuge Not Supporting | 48,791 |
| Mono Lake Not Supporting | 45,299 |
Peers near Schwan Lake's size or cause load
Similar assessed acres
Nearest filed extents (23 acres here).
- Aunie · 23 acres · MN
- Blueberry · 23 acres · MN
- Sport Lake · 23 acres · WI
- Bellevue Lake · 23 acres · FL
Similar cause load
Nearest listed-cause counts (4 here). Peers already in the acreage column are omitted.
- Agency Lake · 4 causes · OR
- Alachua Sink · 4 causes · FL
- Aldrich Pond · 4 causes · MA
- American Falls Reservoir (Snake River) · 4 causes · ID
What to do with this record
- The listing here is on a fishery use, not on fish consumption, and this state reported no consumption verdict for this reservoir. Your state fish-advisory program is the source for whether the catch is safe to eat. 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 CAL3041205319981209102156. 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.