Missouri reservoir · state assessment record
Lake of the Ozarks
Assessment decisions reported by Missouri to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2026 reporting cycle.
- 59,520
- Assessed acres
- Reservoir
- Water type
This waterbody in one line
Lake of the Ozarks, a reservoir in Missouri, 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 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 not supporting.
- Not Supporting
- overall status
- P100
- Assessed size nationally
- P20
- 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.
Lake of the Ozarks 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: assessed size
The number that most separates Lake of the Ozarks nationally is assessed size: 59,520 acres, larger than 100% of the 38,628 lake-type units with an area on file.
Mixed use determinations
This record splits: Not Supporting on aquatic life, Fully Supporting on recreation. The divergence is inside the designated-use matrix, not a single all-or-nothing label.
Lake of the Ozarks: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Lake of the Ozarks. 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 of the Ozarks 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, Missouri carries 623 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Lake of the Ozarks without modification. See our methodology for reporting-unit limits and gauge linking rules.
The record
Assessment entries
Fully Supporting and Not Supporting are the state's definitive verdicts; other entries mean the use was not conclusively assessed in this cycle.
| Assessment entry | Group | Verdict |
|---|---|---|
| Secondary Contact Recreation | Recreation | Fully Supporting |
| Warm Water Habitat | Aquatic-life or related | Not Supporting |
| Whole Body Contact Recreation - Category a | Recreation | Fully Supporting |
| Human Health Protection | Fish-consumption or fishery | Insufficient Information |
| Industrial Water Supply | Other | Insufficient Information |
| Irrigation | Other | Insufficient Information |
| Livestock and Wildlife Protection | Aquatic-life or related | Insufficient Information |
| Unclassified with General Criteria Protections | Other | Insufficient Information |
Not every entry above is a designated use: Unclassified with General Criteria Protections is a record that the water carries no classified designated use. The state files it in the ATTAINS use column, so it carries whatever verdict the state recorded against it.
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 |
|---|---|---|---|
| Chlorophyll-a | Warm Water Habitat | 2020 | TMDL priority: Medium |
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.
- Chlorophyll-a
- Non-Point Source (suspected)
Reading the record
Where Lake of the Ozarks sits among peers
70% of Missouri's lakes assessed this deeply also came out mixed
Missouri ruled definitively on 3 designated uses at Lake of the Ozarks and found 1 of 3 not supported. The dataset shows 23 Missouri lakes judged to that same depth.
Missouri's assessed lakes are most often judged on 1 use; this one was judged on 3.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 89 | 18 | 7 | 3 | 1 |
| Mixed | Not possible | 36 | 16 (this record) | 10 | 3 |
| None supported | 75 | 11 | 0 | 0 | 0 |
Ringed cell: Lake of the Ozarks. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Lake of the Ozarks is one of 623 lake-type waterbodies reported to EPA from Missouri, and one of 170 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 59,520 assessed acres it ranks 46th 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 45 lakes with a larger one.
Not yet on record
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.
Why no water-level record
Lake of the Ozarks 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 of the Ozarks 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
59,520 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 of the Ozarks. Hover or tap any bar for its full count and share.
In context
Missouri context
ATTAINS carries 623 lake-type waterbodies in Missouri, 151 assessed as not supporting at least one use and 118 fully supporting. Among the 170 indexed units there, Lake of the Ozarks ranks 29th by listed-cause count (one listed cause) and 1st by assessed size among the 170 with an area filed; it sits in the not-supporting set (151 statewide) . Its listed causes include Chlorophyll-a, which also appears among Missouri's most-filed impairment causes (led by Chlorophyll-a).
| Other large assessed lakes in Missouri | Assessed acres |
|---|---|
| Harry S Truman Reservoir Not Supporting | 55,600 |
| Table Rock Lake Not Supporting | 41,747 |
| Stockton Lake Fully Supporting | 23,680 |
| Mark Twain Lake Not Supporting | 20,100 |
| Bull Shoals Lake Not Supporting | 9,000 |
| Lake Wappapello Not Supporting | 7,827 |
Peers near Lake of the Ozarks's size or cause load
Similar assessed acres
Nearest filed extents (59,520 acres here).
- Lake Okeechobee · 59,818 acres · FL
- Kenai Lake · 57,618 acres · AK
- Flathead Lake · 57,305 acres · MT
- Champ-Northeast Arm · 57,022 acres · VT
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 MO_7205.00. 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.