Michigan lake · state assessment record
St. Marys River (3,105 acres)
Assessment decisions reported by Michigan to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2020 reporting cycle.
- 3,105
- Assessed acres
- Lake, Freshwater
- Water type
This waterbody in one line
St. Marys River, a lake in Michigan, is assessed as not supporting one or more designated uses, with 5 listed impairment causes in the state's most recent Integrated Report cycle (2020). By assessed acreage it sits among the largest 5% by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (5 listed causes vs 23,610 assessed lakes). Michigan rules it not supporting for other indigenous aquatic life and wildlife, while other aquatic-life uses are supported. Fish consumption is assessed as not supporting.
- Not Supporting
- overall status
- P98
- Assessed size nationally
- P1
- Shorter cause list
- Not Supporting
- aquatic-life or related
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.
Where St. Marys River stands in the filed 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 Michigan, cause-list rank is the local separator: St. Marys River is 16 of 776 indexed units by listed-cause count, toward the top of that state's filed lists.
Large assessed unit
At 3,105 acres, St. Marys River clears the upper tercile of assessed lake-type units with an area on file (969 still larger). Size comparisons use the portal's deduplicated lake ranking population, not raw ATTAINS row counts.
Longer than most cause lists
5 listed causes puts this unit above 97% 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, fish consumption, recreation, 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. Marys River: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for St. Marys River. Read the listed causes and any cleanup actions filed beside them before treating the overall status tile as a finished restoration story.
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. Marys River 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. For the definitive verdicts on this record, Michigan filed the assessment basis as Monitored Data. Those are EPA's own words, not PlainLakes' summary of them. Michigan filed its own confidence on the 9 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 |
| Partial Body Contact Recreation | Recreation | Not Supporting Filer confidence: Good |
| Public Water Supply | Drinking-water supply designation | Fully Supporting Filer confidence: Good |
| Total Body Contact Recreation | Recreation | Not Supporting Filer confidence: Good |
| Warm Water Fishery | Aquatic-life or related | Fully Supporting Filer confidence: Good |
| Cold Water Fishery | Aquatic-life or related | 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 |
|---|---|---|---|
| Mercury in Fish Tissue | Fish Consumption | 1998 | TMDL priority: Low |
| PCBs in Fish Tissue | Fish Consumption | 2006 | TMDL priority: Low |
| Escherichia coli (E. coli) | Partial Body Contact Recreation, Total Body Contact Recreation | 2008 | 4B Restoration Approach |
| Polychlorinated Biphenyls (PCBs) | Other Indigenous Aquatic Life and Wildlife; Fish Consumption | 2008 | None reported |
| Perfluorooctane Sulfonate (PFOS) in Fish Tissue | Fish Consumption | 2024 | 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.
- Mercury in Fish Tissue
- Atmospheric Deposition - Toxics (confirmed)
- PCBs in Fish Tissue
- Atmospheric Deposition - Toxics (confirmed)
- Escherichia coli (E. coli)
- Combined Sewer Overflows (confirmed)
- Polychlorinated Biphenyls (PCBs)
- 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, and Perfluorooctane Sulfonate (PFOS) in Fish Tissue.
Reading the record
Where St. Marys River sits among peers
56% of Michigan's lakes assessed this deeply also came out mixed
Michigan ruled definitively on 9 designated uses at St. Marys River and found 4 of 9 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 9.
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. Marys River. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
St. Marys River 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 3,105 assessed acres it ranks 970th 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 969 lakes with a larger one.
In context
Where St. Marys River 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
3,105 Top 2% larger than 98% 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
5 Longer than most more listed causes than 97% 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. Marys River. 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. Marys River ranks 16th by listed-cause count (5 listed causes) and 34th 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, Escherichia coli (E. coli), 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 Polychlorinated Biphenyls (PCBs), 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. Marys River's size or cause load
Similar assessed acres
Nearest filed extents (3,105 acres here).
- Coyote Lake · 3,106 acres · OR
- Squaw Creek Reservoir · 3,103 acres · TX
- New Hope River Arm of B. Everett Jordan Lake (below normal pool elevation) · 3,101 acres · NC
- El Vado Reservoir · 3,108 acres · NM
Similar cause load
Nearest listed-cause counts (5 here). Peers already in the acreage column are omitted.
- Alexandria Lake No. 3 · 5 causes · NE
- Alexauken Ck (above 74d 55m) · 5 causes · NJ
- Alexauken Ck (below 74d 55m to 11BA06) · 5 causes · NJ
- Alloway Ck (Quinton to Alloway-WdstwnRd) · 5 causes · NJ
What to do with this record
- The fish-consumption use is assessed as not supporting. Before eating fish from this lake, 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 MI040700010302-01. 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.