Michigan reservoir · state assessment record
St. Louis Impoundment
Assessment decisions reported by Michigan to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2018 reporting cycle.
- 129
- Assessed acres
- Reservoir
- Water type
This waterbody in one line
St. Louis Impoundment, a reservoir in Michigan, is assessed as not supporting one or more designated uses, with 8 listed impairment causes in the state's most recent Integrated Report cycle (2018). By assessed acreage it sits in the upper quartile by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (8 listed causes vs 23,610 assessed lakes). Aquatic life is assessed as not supporting. Fish consumption is assessed as not supporting.
- Not Supporting
- overall status
- P75
- Assessed size nationally
- P0
- 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.
Reading St. Louis Impoundment'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 Michigan, cause-list rank is the local separator: St. Louis Impoundment is 2 of 776 indexed units by listed-cause count, toward the top of that state's filed lists.
Longer than most cause lists
8 listed causes puts this unit above 99% 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.
No ruled-on use clears the bar
On the uses this filer ruled on, fish consumption, aquatic life, every determination is Not Supporting. That is a use-by-use reading of the filed record, not a single overall lake grade.
St. Louis Impoundment: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for St. Louis Impoundment. 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 St. Louis Impoundment is Not Supporting. That tile summarizes the assessment unit; the designated-use rows and cause list are the evidence behind it.
According to the U.S. Environmental Protection Agency's ATTAINS program, Michigan carries 4,307 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to St. Louis Impoundment 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. Michigan filed its own confidence on the 5 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 |
|---|---|---|
| Agriculture | Other | Fully Supporting Filer confidence: Good |
| Fish Consumption | Fish-consumption or fishery | Not Supporting Filer confidence: Good |
| Industrial Water Supply | Other | Fully Supporting Filer confidence: Good |
| Navigation | Other | Fully Supporting Filer confidence: Good |
| Other Indigenous Aquatic Life and Wildlife | Aquatic-life or related | Not Supporting Filer confidence: Good |
| Cold Water Fishery | Aquatic-life or related | Not Assessed |
| Partial Body Contact Recreation | Recreation | Not Assessed |
| Total Body Contact Recreation | Recreation | Not Assessed |
| Warm Water Fishery | Aquatic-life or related | Not Assessed |
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 |
|---|---|---|---|
| Polybrominated Biphenyls | Fish Consumption | 1994 | 4B Restoration Approach |
| DDT (Dichlorodiphenyltrichloroethane) | Fish Consumption | 1996 | 4B Restoration Approach |
| Mercury in Water Column | Other Indigenous Aquatic Life and Wildlife | 2008 | TMDL approved |
| Mercury in Fish Tissue | Fish Consumption | 2010 | TMDL approved |
| PCBs in Fish Tissue | Fish Consumption | 2010 | TMDL approved |
| DDT in Fish Tissue | Fish Consumption | 2022 | TMDL priority: Low |
| Dioxin in Fish Tissue | Fish Consumption | 2022 | TMDL priority: Low |
| Perfluorooctane Sulfonate (PFOS) in Fish Tissue | Fish Consumption | 2026 | TMDL priority: Low |
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.
- Polybrominated Biphenyls
- Atmospheric Deposition - Toxics (confirmed)
- DDT (Dichlorodiphenyltrichloroethane)
- Contaminated Sediments (confirmed) Atmospheric Deposition - Toxics (confirmed)
- Mercury in Fish Tissue
- Atmospheric Deposition - Toxics (confirmed)
- PCBs in Fish Tissue
- Contaminated Sediments (confirmed) Atmospheric Deposition - Toxics (confirmed)
Michigan also recorded the source of at least one listing here as unknown, including for Mercury in Fish Tissue, PCBs in Fish Tissue, DDT in Fish Tissue, and Perfluorooctane Sulfonate (PFOS) in Fish Tissue.
Reading the record
Where St. Louis Impoundment sits among peers
56% of Michigan's lakes assessed this deeply also came out mixed
Michigan ruled definitively on 5 designated uses at St. Louis Impoundment and found 2 of 5 not supported. The dataset shows 1,091 Michigan lakes judged to that same depth.
Michigan's assessed lakes are most often judged on 3 uses; this one was judged on 5.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
| 1 | 2 | 3 | 4 | 5+ | |
|---|---|---|---|---|---|
| All supported | 142 | 85 | 1.9k | 822 | 481 |
| Mixed | Not possible | 38 | 0 | 151 | 610 (this record) |
| None supported | 2 | 6 | 0 | 0 | 0 |
Ringed cell: St. Louis Impoundment. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
St. Louis Impoundment is one of 4,307 lake-type waterbodies reported to EPA from Michigan, and one of 776 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 129 assessed acres it ranks 9,870th 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 9,869 lakes with a larger one.
Awaiting a filing
The state has not yet filed a definitive recreation verdict for this record; that field populates when it reports it in a future Integrated Report cycle.
In context
Where St. Louis Impoundment 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
129 Top 25% larger than 75% 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
8 Longer than most more listed causes than 99% 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 St. Louis Impoundment. Hover or tap any bar for its full count and share.
In context
Michigan context
ATTAINS carries 4,307 lake-type waterbodies in Michigan, 807 assessed as not supporting at least one use and 3,457 fully supporting. Among the 776 indexed units there, St. Louis Impoundment ranks 2nd by listed-cause count (8 listed causes) and 333rd by assessed size among the 493 with an area filed; it sits in the not-supporting set (807 statewide) . Its listed causes include Mercury in Fish Tissue, PCBs in Fish Tissue, and Perfluorooctane Sulfonate (PFOS) in Fish Tissue, which also appear among Michigan's most-filed impairment causes (led by Mercury in Fish Tissue). It also lists Polybrominated Biphenyls, DDT (Dichlorodiphenyltrichloroethane), Mercury in Water Column, DDT in Fish Tissue, and Dioxin in Fish Tissue, outside that top-five list.
| Other large assessed lakes in Michigan | Assessed acres |
|---|---|
| Lake Huron (Michigan Jurisdiction) Not Supporting | 5,815,360 |
| Lake Michigan South of Frankfort (Michigan Jurisdiction) Not Supporting | 5,665,920 |
| St. Marys River Not Supporting | 129,983 |
| Lake St. Clair (Michigan Jurisdiction) Not Supporting | 103,616 |
| Lake Erie (Michigan Jurisdiction) Not Supporting | 71,680 |
| Houghton Lake Not Supporting | 20,066 |
Peers near St. Louis Impoundment's size or cause load
Similar assessed acres
Nearest filed extents (129 acres here).
- Portage · 129 acres · MN
- Double (North Portion) · 129 acres · MN
- Halleque · 129 acres · MN
- Beaver Creek Lake (Bear Creek Lake)-02040106001281 · 129 acres · PA
Similar cause load
Nearest listed-cause counts (8 here). Peers already in the acreage column are omitted.
- Ashuelot River - Fisk Mill Hydro · 8 causes · NH
- Assabet River Reservoir · 8 causes · MA
- Billington Sea · 8 causes · MA
- Brownlee Reservoir, Upper (Weiser to Porters Flat) · 8 causes · ID
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 MI040802020403-04. 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.