Idaho lake · state assessment record
Pioneer Reservoir
Assessment decisions reported by Idaho to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2014 reporting cycle.
- 229
- Assessed acres
- Lake, Freshwater
- Water type
This waterbody in one line
Pioneer Reservoir, a lake in Idaho, is assessed as not supporting one or more designated uses, with 5 listed impairment causes in the state's most recent Integrated Report cycle (2014). By assessed acreage it sits in the upper quartile by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (5 listed causes vs 23,610 assessed lakes). Aquatic life is assessed as not supporting.
- Not Supporting
- overall status
- P83
- Assessed size nationally
- P1
- 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.
Pioneer Reservoir against the ATTAINS 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: in-state cause rank
Inside Idaho, cause-list rank is the local separator: Pioneer Reservoir is 4 of 186 indexed units by listed-cause count, toward the top of that state's filed lists.
Longer than most cause lists
5 listed causes puts this unit above 97% of assessed lake-type records by list length. Treat that as a coding-and-sampling signal: states that split pollutants finely mint longer lists without proving worse water.
Every ruled-on use is not supporting
On the uses this filer ruled on, 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.
Pioneer Reservoir: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Pioneer Reservoir. Read the listed causes and any cleanup actions filed beside them before treating the overall status tile as a finished restoration story.
Large assessed unit
At 228.9 acres, Pioneer Reservoir clears the upper tercile of assessed lake-type units with an area on file (6,509 still larger). Size comparisons use the portal's deduplicated lake ranking population, not raw ATTAINS row counts.
According to the U.S. Environmental Protection Agency's ATTAINS program, Idaho carries 630 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Pioneer 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. Idaho filed its own confidence on the 2 definitive verdicts it rated: Good. 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 |
|---|---|---|
| Cold Water Aquatic Life | Aquatic-life or related | Not Supporting Filer confidence: Good |
| Primary Contact Recreation | Recreation | Not Supporting Filer confidence: Good |
| Aesthetic | Other | Not Assessed |
| Agricultural Water Supply | Other | Not Assessed |
| Industrial Water Supply | Other | Not Assessed |
| Wildlife Habitat | Other | Not Assessed |
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 |
|---|---|---|---|
| Escherichia coli (E. coli) | Primary Contact Recreation | 1994 | TMDL priority: High |
| Phosphorus, Total | Cold Water Aquatic Life | 1994 | TMDL approved |
| Temperature | Cold Water Aquatic Life | 1994 | TMDL priority: High |
| Total Suspended Solids (TSS) | Cold Water Aquatic Life | 2006 | TMDL approved |
| Flow Regime Modification | Cold Water Aquatic Life | Not reported | None reported |
Reading the record
Cleanup queue for Pioneer Reservoir
2 listed causes ranked High in the TMDL queue, still without a plan
Idaho ranked 2 listed causes high in its TMDL development queue, and no cleanup plan is on file for those listings yet. That queue rank is the state's own scheduling signal, not an EPA national rule.
A High ranking names a position in the state's plan-writing queue; it is not a measure of how impaired the water is. How listing and cleanup work.
Scale and rank
Pioneer Reservoir is one of 630 lake-type waterbodies reported to EPA from Idaho, and one of 186 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 229 assessed acres it ranks 6,510th 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 6,509 lakes with a larger one.
Awaiting a filing
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.
In context
Where Pioneer 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
229 Top 17% larger than 83% 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
5 Longer than most more listed causes than 97% 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 Pioneer Reservoir. Hover or tap any bar for its full count and share.
In context
Idaho context
ATTAINS carries 630 lake-type waterbodies in Idaho, 51 assessed as not supporting at least one use and 198 fully supporting. Among the 186 indexed units there, Pioneer Reservoir ranks 4th by listed-cause count (5 listed causes) and 47th by assessed size among the 186 with an area filed; it sits in the not-supporting set (51 statewide) . Its listed causes include Phosphorus, Total; and Flow Regime Modification, which also appear among Idaho's most-filed impairment causes (led by Phosphorus, Total). It also lists Escherichia coli (E. coli), Temperature, and Total Suspended Solids (TSS), outside that top-five list.
| Other large assessed lakes in Idaho | Assessed acres |
|---|---|
| Pend Oreille Lake Not Supporting | 80,829 |
| Bear Lake Not Assessed | 34,454 |
| American Falls Reservoir (Snake River) Not Supporting | 31,724 |
| Cascade Reservoir Not Supporting | 25,040 |
| American Falls Reservoir (Snake River) Tribal Waters Not Assessed | 23,785 |
| Grays Lake Not Assessed | 23,678 |
Peers near Pioneer Reservoir's size or cause load
Similar assessed acres
Nearest filed extents (229 acres here).
- Stevens · 229 acres · MN
- Fish · 229 acres · MN
- Redwater Lake · 229 acres · FL
- Walker Lake-02050301001348 · 229 acres · PA
Similar cause load
Nearest listed-cause counts (5 here). Peers already in the acreage column are omitted.
- Alexandria Lake No. 3 · 5 causes · NE
- Alexauken Ck (above 74d 55m) · 5 causes · NJ
- Alexauken Ck (below 74d 55m to 11BA06) · 5 causes · NJ
- Alloway Ck (Quinton to Alloway-WdstwnRd) · 5 causes · NJ
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 ID17040212SK035_04. 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.