Iowa lake · state assessment record
Lake Darling
Assessment decisions reported by Iowa to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2024 reporting cycle, a cycle that carries an interim EPA action.
- 299
- Assessed acres
- Lake
- Water type
- Eutrophic
- Reported trophic class
This waterbody in one line
Lake Darling, a lake in Iowa, is assessed as not supporting one or more designated uses, with 4 listed impairment causes in the state's most recent Integrated Report cycle (2024), a cycle that carries an interim EPA action. By assessed acreage it sits in the upper quartile by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (4 listed causes vs 23,610 assessed lakes).
- Not Supporting
- overall status
- P86
- Assessed size nationally
- P3
- Shorter cause list
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 Darling'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: in-state cause rank
Inside Iowa, cause-list rank is the local separator: Lake Darling is 4 of 167 indexed units by listed-cause count, toward the top of that state's filed lists.
Longer than most cause lists
4 listed causes puts this unit above 95% 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 filed use falls short
On the uses this filer ruled on, recreation, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
Lake Darling: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Lake Darling. 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 299 acres, Lake Darling clears the upper tercile of assessed lake-type units with an area on file (5,377 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, Iowa carries 371 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Lake Darling 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 |
|---|---|---|
| Drinking Water | Drinking-water supply designation | Fully Supporting |
| Primary Contact Recreation | Recreation | Not Supporting |
| Aquatic Life - Lakes and Wetlands Warmwater | Aquatic-life or related | Insufficient Information |
| Human Health | Recreation | Insufficient Information |
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 |
|---|---|---|---|
| Turbidity | Primary Contact Recreation | 2002 | TMDL approved |
| pH | Aquatic Life - Lakes and Wetlands Warmwater; Primary Contact Recreation | 2008 | TMDL approved |
| Escherichia coli (E. coli) | Primary Contact Recreation | 2018 | TMDL priority: Medium |
| Chlorophyll-a | Primary Contact Recreation | 2020 | TMDL approved |
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.
- Turbidity
- Sediment Resuspension (Clean Sediment) (suspected)
- pH
- Internal Nutrient Recycling (suspected)
Iowa also recorded the source of at least one listing here as unknown, including for Escherichia coli (E. coli).
Reading the record
Where Lake Darling sits among peers
49% of Iowa's lakes assessed this deeply also came out mixed
Iowa ruled definitively on 2 designated uses at Lake Darling and found 1 of 2 not supported. The dataset shows 77 Iowa lakes judged to that same depth.
Iowa's assessed lakes are most often judged on 2 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 | 27 | 27 | 10 | 2 | 0 |
| Mixed | Not possible | 38 (this record) | 31 | 7 | 0 |
| None supported | 45 | 12 | 4 | 0 | 0 |
Ringed cell: Lake Darling. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Lake Darling is one of 371 lake-type waterbodies reported to EPA from Iowa, and one of 167 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 299 assessed acres it ranks 5,378th 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 5,377 lakes with a larger one.
Not yet on record
The state has not yet filed a definitive fish-consumption verdict and a definitive aquatic-life verdict for this record; those fields populate when it reports them 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.
In context
Where Lake Darling 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
299 Top 14% larger than 86% 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
4 Longer than most more listed causes than 95% 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 Darling. Hover or tap any bar for its full count and share.
In context
Iowa context
ATTAINS carries 371 lake-type waterbodies in Iowa, 137 assessed as not supporting at least one use and 66 fully supporting. Among the 167 indexed units there, Lake Darling ranks 4th by listed-cause count (4 listed causes) and 51st by assessed size among the 167 with an area filed; it sits in the not-supporting set (137 statewide) . Its listed causes include Turbidity, pH, Escherichia coli (E. coli), and Chlorophyll-a, which also appear among Iowa's most-filed impairment causes (led by Chlorophyll-a).
| Other large assessed lakes in Iowa | Assessed acres |
|---|---|
| Red Rock Reservoir Not Supporting | 19,000 |
| Rathbun Reservoir - Main Basin Fully Supporting | 6,330 |
| Saylorville Reservoir Not Supporting | 5,950 |
| Coralville Reservoir Not Supporting | 4,900 |
| Big Spirit Lake Fully Supporting | 4,169 |
| Clear Lake Not Supporting | 3,684 |
Peers near Lake Darling's size or cause load
Similar assessed acres
Nearest filed extents (299 acres here).
- Wheatgrass Lake · 299 acres · OR
- Sabin · 299 acres · MN
- George · 300 acres · MN
- Pine Lake · 300 acres · WI
Similar cause load
Nearest listed-cause counts (4 here). Peers already in the acreage column are omitted.
- Agency Lake · 4 causes · OR
- Alachua Sink · 4 causes · FL
- Aldrich Pond · 4 causes · MA
- American Falls Reservoir (Snake River) · 4 causes · ID
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 IA 03-SKU-924. 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.