North Dakota reservoir · state assessment record
Lake Sakakawea
Assessment decisions reported by North Dakota to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2012 reporting cycle.
- 318,821
- Assessed acres
- Reservoir
- Water type
- Mesotrophic
- Reported trophic class
This waterbody in one line
Lake Sakakawea, a reservoir in North Dakota, is assessed as not supporting one or more designated uses, with one listed impairment cause in the state's most recent Integrated Report cycle (2012). By assessed acreage it sits among the largest 1% of assessed lakes nationally (38,628 lakes with a filed area); its impairment list is among the longest nationally (one listed cause vs 23,610 assessed lakes). Aquatic life is assessed as fully supporting. Fish consumption is assessed as not supporting.
- Not Supporting
- overall status
- P100
- 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.
Reading Lake Sakakawea'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: assessed size
The number that most separates Lake Sakakawea nationally is assessed size: 318,821 acres, larger than 100% of the 38,628 lake-type units with an area on file.
The uses disagree
This record splits: Not Supporting on fish consumption, Fully Supporting on recreation, aquatic life. The divergence is inside the designated-use matrix, not a single all-or-nothing label.
Lake Sakakawea: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Lake Sakakawea. 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 Lake Sakakawea 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, North Dakota carries 340 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Lake Sakakawea 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. North Dakota filed its own confidence on the 6 definitive verdicts it rated: Fair, Good and Excellent. 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 Consumption | Fish-consumption or fishery | Not Supporting Filer confidence: Excellent |
| Fish and Other Aquatic Biota | Aquatic-life or related | Fully Supporting Filer confidence: Excellent |
| Industrial | Other | Fully Supporting Filer confidence: Good |
| Municipal and Domestic | Drinking-water supply designation | Fully Supporting Filer confidence: Fair on other public health indicators; Excellent on physical/chemical |
| Recreation | Recreation | Fully Supporting Filer confidence: Excellent |
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 |
|---|---|---|---|
| Methylmercury | Fish Consumption | 2002 | TMDL priority: Low |
Reading the record
Where Lake Sakakawea sits among peers
4 of 8 North Dakota lakes assessed this deeply also came out mixed
North Dakota ruled definitively on 6 designated uses at Lake Sakakawea and found 1 of 6 not supported. The dataset shows 8 North Dakota lakes judged to that same depth.
North Dakota's assessed lakes are most often judged on 4 uses; this one was judged on 6.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 0 | 19 | 3 | 154 | 4 |
| Mixed | Not possible | 0 | 1 | 10 | 4 (this record) |
| None supported | 0 | 0 | 0 | 0 | 0 |
Ringed cell: Lake Sakakawea. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Lake Sakakawea 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 318,821 assessed acres it ranks 9th 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 8 lakes with a larger one.
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.
Why no water-level record
Lake Sakakawea 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 Sakakawea 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
318,821 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
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 Lake Sakakawea. 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 Sakakawea ranks 31st by listed-cause count (one listed cause) and 1st by assessed size among the 174 with an area filed; it sits in the not-supporting set (52 statewide) . Its listed causes include Methylmercury, which also appears among North Dakota's most-filed impairment causes (led by Nutrients).
| Other large assessed lakes in North Dakota | Assessed acres |
|---|---|
| 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 |
| Pelican Lake Not reported | 13,491 |
Peers near Lake Sakakawea's size or cause load
Similar assessed acres
Nearest filed extents (318,821 acres here).
- Lake of the Woods · 301,348 acres · MN
- Lake of the Woods (Main) · 301,348 acres · MN
- Lake Erie Western Basin Open Water (>3m) · 337,472 acres · OH
- Gunnison Bay · 384,588 acres · UT
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
- The fish-consumption use is assessed as not supporting. Before eating fish from this reservoir, check your state fish-advisory program for species-specific meal limits. 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-10110101-021-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.