Louisiana lake · state assessment record
Cypress Bayou Reservoir
Assessment decisions reported by Louisiana to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2026 reporting cycle.
- 2,841
- Assessed acres
- Lake, Freshwater
- Water type
This waterbody in one line
Cypress Bayou Reservoir, a lake in Louisiana, 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 5% 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 fully supporting.
- Not Supporting
- overall status
- P97
- Assessed size nationally
- P20
- Shorter cause list
- Fully 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.
How Cypress Bayou Reservoir reads against 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 Cypress Bayou Reservoir nationally is assessed size: 2,841 acres, larger than 97% of the 38,628 lake-type units with an area on file.
Cypress Bayou Reservoir: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Cypress Bayou Reservoir. Read the listed causes and any cleanup actions filed beside them before treating the overall status tile as a finished restoration story.
Every filed use clears the bar
The filed use determinations for recreation, aquatic life are all Fully Supporting. Where an overall IR category still flags the unit, look at the cause list and report standing rather than treating the use row as empty.
Overall status: not supporting
The filer's overall status for Cypress Bayou Reservoir 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, Louisiana carries 76 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Cypress Bayou Reservoir 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. The latest monitoring Louisiana filed against this record runs through 2023. For the definitive verdicts on this record, Louisiana filed the assessment basis as Monitored Data. Those are EPA's own words, not PlainLakes' summary of them. Louisiana filed its own confidence on the 5 definitive verdicts it rated: Fair. That rating is the filer's, in EPA's own field, and EPA publishes no definition of the four words it offers.
| Designated use | Group | Verdict |
|---|---|---|
| Agriculture | Other | Fully Supporting Filer confidence: Fair |
| Drinking Water Supply | Drinking-water supply designation | Not Supporting Filer confidence: Fair |
| Fish and Wildlife Propagation | Aquatic-life or related | Fully Supporting Filer confidence: Fair |
| Primary Contact Recreation | Recreation | Fully Supporting Filer confidence: Fair |
| Secondary Contact Recreation | Recreation | Fully Supporting Filer confidence: Fair |
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 |
|---|---|---|---|
| Color | Drinking Water Supply | 2004 | TMDL priority: Low |
Probable sources named by the state
Each source below is listed under the cause the state filed it against, and carries the word the state filed with it — confirmed, or suspected.
- Color
- Natural Sources (suspected)
Reading the record
Where Cypress Bayou Reservoir sits among peers
6 of 6 Louisiana lakes assessed this deeply also came out mixed (every lake judged to this depth, so the outcome does not set this record apart)
Louisiana ruled definitively on 5 designated uses at Cypress Bayou Reservoir and found 1 of 5 not supported. The dataset shows 6 Louisiana lakes judged to that same depth.
Louisiana's assessed lakes are most often judged on 3 uses; this one was judged on 5.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 1 | 0 | 8 | 2 | 0 |
| Mixed | Not possible | 4 | 31 | 11 | 6 (this record) |
| None supported | 12 | 0 | 0 | 0 | 0 |
Ringed cell: Cypress Bayou Reservoir. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Cypress Bayou Reservoir is one of 76 lake-type waterbodies reported to EPA from Louisiana, and one of 74 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 2,841 assessed acres it ranks 1,039th 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 1,038 lakes with a larger one.
Still unfiled
The state has not yet filed a definitive fish-consumption verdict for this record; that field populates when it reports it in a future Integrated Report cycle.
Reported trophic class
Louisiana 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.
In context
Where Cypress Bayou Reservoir 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
2,841 Top 3% larger than 97% 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 Cypress Bayou Reservoir. Hover or tap any bar for its full count and share.
In context
Louisiana context
ATTAINS carries 76 lake-type waterbodies in Louisiana, 64 assessed as not supporting at least one use and 11 fully supporting. Among the 74 indexed units there, Cypress Bayou Reservoir ranks 43rd by listed-cause count (one listed cause) and 28th by assessed size among the 74 with an area filed; it sits in the not-supporting set (64 statewide) . Its listed causes (Color) sit outside Louisiana's top-five list, which is led by Mercury - Fish Consumption Advisory.
| Other large assessed lakes in Louisiana | Assessed acres |
|---|---|
| Toledo Bend Reservoir-From Texas-Louisiana state line to Toledo Bend Dam Not Supporting | 165,487 |
| White Lake Not Supporting | 56,487 |
| Lake Salvador Not Supporting | 49,477 |
| Grand Lake Not Supporting | 47,869 |
| Lac Des Allemands Not Supporting | 16,596 |
| Catahoula Lake Not Supporting | 16,509 |
Peers near Cypress Bayou Reservoir's size or cause load
Similar assessed acres
Nearest filed extents (2,841 acres here).
- Herrington Lake · 2,847 acres · KY
- Georgetown Lake · 2,834 acres · MT
- Whitney Lake · 2,851 acres · TX
- Ashley Lake · 2,852 acres · MT
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 LA100404_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.