Montana lake · state assessment record
Hebgen Lake
The assessment record reported by Montana to EPA under Clean Water Act sections 303(d) and 305(b), filed in the 2000 reporting cycle.
- 12,407
- Assessed acres
- Lake, Freshwater
- Water type
- Mesotrophic
- Reported trophic class
- 6,531.5 ft
- Water Surface Elevation (provisional)
This waterbody in one line
Hebgen Lake, a lake in Montana, was reported but not assessed in the state's most recent Integrated Report cycle (2000). By assessed acreage it sits among the largest 1% of assessed lakes nationally (38,628 lakes with a filed area). A USGS gauge tracks its water surface elevation daily.
- Not Assessed
- overall status
- P99
- Assessed size nationally
Assessment verdicts are the state agency's decisions as reported to EPA ATTAINS; PlainLakes renders them without modification.
Where Hebgen Lake 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 Hebgen Lake nationally is assessed size: 12,407 acres, larger than 99% of the 38,628 lake-type units with an area on file.
IR category 3 on Hebgen Lake
The Integrated Report category filed for Hebgen Lake is 3. PlainLakes renders EPA's code without remapping it into a consumer grade.
Overall status: Not Assessed
ATTAINS overall status on this unit is “Not Assessed”. PlainLakes does not rewrite that vocabulary into a consumer score.
According to the U.S. Environmental Protection Agency's ATTAINS program, Montana carries 73 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Hebgen 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 |
|---|---|---|
| Agricultural | Other | Not Assessed |
| Aquatic Life | Aquatic-life or related | Not Assessed |
| Drinking Water | Drinking-water supply designation | Not Assessed |
| Primary Contact Recreation | Recreation | Not Assessed |
The record
Listed impairment causes
The state reported this lake in its 2000 Integrated Report cycle but reached no assessment determination, so no causes are listed. The unit is recorded under EPA integrated-reporting Category 3: reviewed, with insufficient information to determine whether it meets water-quality standards. An undetermined waterbody is neither confirmed clean nor confirmed impaired.
Reading the record
What Hebgen Lake's record holds
Scale and rank
Hebgen Lake is one of 73 lake-type waterbodies reported to EPA from Montana. It is not among the 52 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 12,407 assessed acres it ranks 258th 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 257 lakes with a larger one.
Water level
A USGS gauge tracks this lake's water surface elevation daily, and the latest reading is 2.53 ft below the reading 30 days earlier, against a 365-day observed range of 6.1 ft. The state has not yet filed a definitive fish-consumption verdict, a definitive recreation verdict, a definitive aquatic-life verdict, and 1 other for this record; those fields populate when it reports them in a future Integrated Report cycle.
Reported trophic class
Mesotrophic is the trophic class the filing agency reported to EPA ATTAINS for this assessment unit. It describes nutrient enrichment, not whether the water is safe, and it is not a PlainLakes inference. What the trophic scale measures.
Water level: 365-day record
Daily water surface elevation values, feet above the National Geodetic Vertical Datum of 1929 (NGVD 29), from USGS gauge 06038000 (Hebgen Lake Near West Yellowstone, Mt), shown weekly. Readings are daily-batch snapshots, not real-time conditions. Each daily value is a single reading taken at 24:00, not a daily mean. It is the only daily statistic USGS files for this gauge.
- Latest reading
- 6,531.5 ft 2.5299999999997453ft vs 30 days earlier
- 2026-08-15 · Provisional, subject to USGS revision
Water level: 365-day record
Subscribe to water level updates for Hebgen Lake (RSS)
171 of the 364 daily values in this window (47%) are provisional and subject to USGS revision; USGS has approved this gauge's record through 2026-02-25.
Full gauge record: USGS monitoring location 06038000
In context
Where Hebgen 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
12,407 Top 1% larger than 99% 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
In both charts each bar is a band and taller bars hold more waterbodies; the dashed line and filled bar mark Hebgen Lake. Hover or tap any bar for its full count and share.
In context
Montana context
ATTAINS carries 73 lake-type waterbodies in Montana, 28 assessed as not supporting at least one use and 28 fully supporting.
| Other large assessed lakes in Montana | Assessed acres |
|---|---|
| Fort Peck Reservoir Not Supporting | 233,296 |
| Flathead Lake Not Supporting | 57,305 |
| Canyon Ferry Reservoir Not Supporting | 32,810 |
| Lake Koocanusa Not Supporting | 28,875 |
| Hungry Horse Reservoir Fully Supporting | 23,596 |
| Lake Elwell (Tiber Reservoir) Fully Supporting | 15,041 |
Lakes near Hebgen Lake's assessed acres
Similar assessed acres
Nearest filed extents (12,407 acres here).
- Castle Rock Lake · 12,386 acres · WI
- West Branch Penobscot River (4) · 12,365 acres · ME
- Fort Gibson Lake · 12,464 acres · OK
- O. H. Ivie Reservoir · 12,350 acres · TX
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
- Water levels shown are daily snapshots. Seasonal drawdown and datum conventions matter when comparing levels. How to read level data
- 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 MT41F005_010. 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.