North Dakota lake · state assessment record
Lake Isabel
Assessment decisions reported by North Dakota to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2018 reporting cycle.
- 827
- Assessed acres
- Lake, Natural
- Water type
- Eutrophic
- Reported trophic class
This waterbody in one line
Lake Isabel, a lake in North Dakota, is assessed as not supporting one or more designated uses, with 2 listed impairment causes in the state's most recent Integrated Report cycle (2018). By assessed acreage it sits among the largest 10% by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (2 listed causes vs 23,610 assessed lakes). Aquatic life is assessed as fully supporting, and flagged threatened: currently met, but on a trajectory the state expects to fail.
- Not Supporting
- overall status
- P93
- Assessed size nationally
- P10
- Shorter cause list
- Fully Supporting
- aquatic life, threatened
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.
Lake Isabel 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 North Dakota, cause-list rank is the local separator: Lake Isabel is 11 of 174 indexed units by listed-cause count, toward the top of that state's filed lists.
Large assessed unit
At 827.3 acres, Lake Isabel clears the upper tercile of assessed lake-type units with an area on file (2,582 still larger). Size comparisons use the portal's deduplicated lake ranking population, not raw ATTAINS row counts.
Lake Isabel: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Lake Isabel. Read the listed causes and any cleanup actions filed beside them before treating the overall status tile as a finished restoration story.
All ruled-on uses pass
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.
Longer than most cause lists
2 listed causes puts this unit above 80% 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.
According to the U.S. Environmental Protection Agency's ATTAINS program, North Dakota carries 340 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Lake Isabel 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 North Dakota filed against this record runs through 2016. For the definitive verdicts on this record, North Dakota filed the assessment basis as Monitored Data. Those are EPA's own words, not PlainLakes' summary of them. North Dakota filed its own confidence on the 4 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 |
|---|---|---|
| Agricultural | Other | Fully Supporting Filer confidence: Good |
| Fish and Other Aquatic Biota threatened | Aquatic-life or related | Fully Supporting Filer confidence: Good |
| Industrial | Other | Fully Supporting Filer confidence: Good |
| Recreation threatened | Recreation | Fully Supporting Filer confidence: Good |
| Fish Consumption | Fish-consumption or fishery | Not Assessed |
| Municipal and Domestic | Drinking-water supply designation | 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 |
|---|---|---|---|
| Dissolved Oxygen | Fish and Other Aquatic Biota | 1992 | TMDL priority: Low |
| Eutrophication, Nutrients | Recreation; Fish and Other Aquatic Biota | 2018 | TMDL priority: Low |
Reading the record
Where Lake Isabel sits among peers
94% of North Dakota's lakes assessed this deeply were also judged fully supported (the standard result at this depth, not a distinction)
North Dakota ruled definitively on 4 designated uses at Lake Isabel and found every one of them supported, though the state recorded the causes below as not meeting criteria for Fish and Other Aquatic Biota and Recreation. The dataset shows 164 North Dakota lakes judged to that same depth.
North Dakota's assessed lakes are most often judged on 4 uses, as this one was.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 0 | 19 | 3 | 154 (this record) | 4 |
| Mixed | Not possible | 0 | 1 | 10 | 4 |
| None supported | 0 | 0 | 0 | 0 | 0 |
Ringed cell: Lake Isabel. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Lake Isabel is one of 340 lake-type waterbodies reported to EPA from North Dakota, and one of 174 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 827 assessed acres it ranks 2,583rd 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 2,582 lakes with a larger one.
Open in the register
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
Eutrophic 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.
Why no water-level record
Lake Isabel has no daily USGS water-level or reservoir-storage series on this page because NWIS lists a lake monitoring site named for the waterbody, but the site is not active, and PlainLakes ingests only the active inventory, so there is no series to attach. How PlainLakes links gauges.
In context
Where Lake Isabel 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
827 Top 7% larger than 93% 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
2 Longer than most more listed causes than 80% 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 Isabel. Hover or tap any bar for its full count and share.
In context
North Dakota context
ATTAINS carries 340 lake-type waterbodies in North Dakota, 52 assessed as not supporting at least one use and 143 fully supporting. Among the 174 indexed units there, Lake Isabel ranks 11th by listed-cause count (2 listed causes) and 26th by assessed size among the 174 with an area filed; it sits in the not-supporting set (52 statewide) . Its listed causes include Dissolved Oxygen; and Eutrophication, Nutrients, which also appear among North Dakota's most-filed impairment causes (led by Nutrients).
| Other large assessed lakes in North Dakota | Assessed acres |
|---|---|
| Lake Sakakawea Not Supporting | 318,821 |
| Devils Lake Not Supporting | 102,385 |
| Lake Oahe Fully Supporting | 68,123 |
| Little Missouri Bay (Lake Sakakawea) Not Supporting | 22,719 |
| Long Lake Refuge Not reported | 16,990 |
| Lake Audubon Fully Supporting | 16,610 |
Peers near Lake Isabel's size or cause load
Similar assessed acres
Nearest filed extents (827 acres here).
- Big Lake · 827 acres · WI
- Crooked Lake · 828 acres · IN
- Great Averill · 828 acres · VT
- Upper Saint Croix Lake · 828 acres · WI
Similar cause load
Nearest listed-cause counts (2 here). Peers already in the acreage column are omitted.
- 12th St. Beach · 2 causes · IL
- 31st St. Beach · 2 causes · IL
- 49th St. Beach · 2 causes · IL
- 57th St. Beach · 2 causes · IL
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 ND-10130103-010-L_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.