Michigan reservoir · state assessment record
C. S. Mott Lake (Reservoir)
NE of Flint. Genessee Co. Assessment decisions reported by Michigan to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2024 reporting cycle.
- 600
- Assessed acres
- Reservoir
- Water type
- Hypereutrophic
- Reported trophic class
This waterbody in one line
C. S. Mott Lake (Reservoir), a reservoir 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 (2024). By assessed acreage it sits among the largest 10% by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (5 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
- P92
- Assessed size nationally
- P1
- 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.
How C. S. Mott Lake (Reservoir) reads against 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: C. S. Mott Lake (Reservoir) is 18 of 776 indexed units by listed-cause count, toward the top of that state's filed lists.
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.
Large assessed unit
At 600.2 acres, C. S. Mott Lake (Reservoir) clears the upper tercile of assessed lake-type units with an area on file (3,289 still larger). Size comparisons use the portal's deduplicated lake ranking population, not raw ATTAINS row counts.
C. S. Mott Lake (Reservoir): Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for C. S. Mott Lake (Reservoir). 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 C. S. Mott Lake (Reservoir) 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 7 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 |
| Total Body Contact Recreation | Recreation | Not Supporting Filer confidence: Good |
| Cold Water Fishery | Aquatic-life or related | 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 |
|---|---|---|---|
| Escherichia coli (E. coli) | Total Body Contact Recreation, Partial Body Contact Recreation | 2012 | TMDL approved |
| PCBs in Fish Tissue | Fish Consumption | 2020 | TMDL approved |
| Perfluorooctane Sulfonate (PFOS) in Fish Tissue | Fish Consumption | 2020 | TMDL priority: Low |
| Eutrophication, Nutrients | Other Indigenous Aquatic Life and Wildlife | 2024 | TMDL priority: Low |
| Mercury 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.
- Escherichia coli (E. coli)
- Agriculture (suspected) On-Site Treatment Systems (Septic Systems and Similar Decentralized Systems) (suspected) Urban Runoff/Storm Sewers (suspected) Sewage Discharges in Unsewered Areas (suspected)
- PCBs in Fish Tissue
- Atmospheric Deposition - Toxics (confirmed)
- Perfluorooctane Sulfonate (PFOS) in Fish Tissue
- Industrial Point Source Discharge (confirmed) Discharges From Biosolids (Sludge) Storage, Application or Disposal (confirmed) Discharges From Municipal Separate Storm Sewer Systems (MS4) (confirmed)
Michigan also recorded the source of at least one listing here as unknown, including for PCBs in Fish Tissue; Perfluorooctane Sulfonate (PFOS) in Fish Tissue; Eutrophication, Nutrients; and Mercury in Fish Tissue.
Reading the record
Where C. S. Mott Lake (Reservoir) sits among peers
56% of Michigan's lakes assessed this deeply also came out mixed
Michigan ruled definitively on 7 designated uses at C. S. Mott Lake (Reservoir) and found 4 of 7 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 7.
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: C. S. Mott Lake (Reservoir). Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
C. S. Mott Lake (Reservoir) 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 600 assessed acres it ranks 3,290th 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 3,289 lakes with a larger one.
Reported trophic class
Hypereutrophic 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 C. S. Mott Lake (Reservoir) 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
600 Top 8% larger than 92% 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 C. S. Mott Lake (Reservoir). 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, C. S. Mott Lake (Reservoir) ranks 18th by listed-cause count (5 listed causes) and 132nd by assessed size among the 493 with an area filed; it sits in the not-supporting set (807 statewide) . Its listed causes include Escherichia coli (E. coli), PCBs in Fish Tissue, Perfluorooctane Sulfonate (PFOS) in Fish Tissue, and Mercury in Fish Tissue, which also appear among Michigan's most-filed impairment causes (led by Mercury in Fish Tissue). It also lists Eutrophication, Nutrients, 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 C. S. Mott Lake (Reservoir)'s size or cause load
Similar assessed acres
Nearest filed extents (600 acres here).
- Stonecoal Reservoir · 600 acres · WV
- Clearwater Lake · 600 acres · AK
- Colleen Lake · 600 acres · AK
- Highland Silver · 600 acres · IL
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 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 MI040802040409-08. 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.