Wisconsin lake · state assessment record
Lake Kegonsa
In Dane County. Assessment decisions reported by Wisconsin to EPA under Clean Water Act sections 303(d) and 305(b), last assessed in the 2026 reporting cycle.
- 3,200
- Assessed acres
- Lake, Freshwater
- Water type
- Eutrophic
- Reported trophic class
- 3.2 ft
- Gage Height (provisional)
This waterbody in one line
Lake Kegonsa, a lake in Wisconsin, is assessed as not supporting one or more designated uses, with 2 listed impairment causes in the state's most recent Integrated Report cycle (2026). By assessed acreage it sits among the largest 5% by assessed acreage nationally (38,628 lakes); its impairment list is among the longest nationally (2 listed causes vs 23,610 assessed lakes). Aquatic life is assessed as not supporting. Fish consumption is assessed as not supporting. A USGS gauge tracks its gage height daily.
- Not Supporting
- overall status
- P98
- Assessed size nationally
- P10
- 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 Lake Kegonsa 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 Wisconsin, cause-list rank is the local separator: Lake Kegonsa is 17 of 1,219 indexed units by listed-cause count, toward the top of that state's filed lists.
Large assessed unit
At 3,200 acres, Lake Kegonsa clears the upper tercile of assessed lake-type units with an area on file (938 still larger). Size comparisons use the portal's deduplicated lake ranking population, not raw ATTAINS row counts.
Every ruled-on use is not supporting
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.
Lake Kegonsa: Category 5, TMDL still owed
Category 5 is the Integrated Report band where a TMDL (or equivalent) is still expected for Lake Kegonsa. Read the listed causes and any cleanup actions filed beside them before treating the overall status tile as a finished restoration story.
Large within Wisconsin
Among Wisconsin's 1,170 indexed units with an area, Lake Kegonsa ranks 31 by assessed size, toward the large end of that state file.
According to the U.S. Environmental Protection Agency's ATTAINS program, Wisconsin carries 19,871 filed lake-type waterbodies in the August 2026 extract, and this page renders the assessment record EPA assigned to Lake Kegonsa 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. The latest monitoring Wisconsin filed against this record runs through 2026. For the definitive verdicts on this record, Wisconsin filed the assessment basis as Monitored Data. Those are EPA's own words, not PlainLakes' summary of them. Wisconsin filed its own confidence on the 3 definitive verdicts it rated: Good and Excellent. 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 |
|---|---|---|
| Fish Consumption | Fish-consumption or fishery | Not Supporting Filer confidence: Excellent |
| Fish and Aquatic Life | Aquatic-life or related | Not Supporting Filer confidence: Good |
| Recreation | Recreation | Not Supporting Filer confidence: Good |
| Public Health and Welfare | Recreation | Not Assessed |
| Wildlife | 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 |
|---|---|---|---|
| Phosphorus, Total | Fish and Aquatic Life; Recreation | 2012 | TMDL approved |
| Perfluorooctane Sulfonate (PFOS) | Fish Consumption | 2022 | 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.
- Phosphorus, Total
- Upstream Source (suspected) Non-Point Source (suspected)
- Perfluorooctane Sulfonate (PFOS)
- Non-Point Source (suspected)
Reading the record
Where Lake Kegonsa sits among peers
8% of Wisconsin's lakes assessed this deeply also had no use supported
Wisconsin ruled definitively on 3 designated uses at Lake Kegonsa and found none of them supported. The dataset shows 253 Wisconsin lakes judged to that same depth.
Wisconsin'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 | 3.5k | 609 | 121 | 1 | 1 |
| Mixed | Not possible | 118 | 112 | 2 | 0 |
| None supported | 78 | 162 | 20 (this record) | 1 | 0 |
Ringed cell: Lake Kegonsa. Source: EPA ATTAINS, Reporting cycles 1987–2026.
Scale and rank
Lake Kegonsa is one of 19,871 lake-type waterbodies reported to EPA from Wisconsin, and one of 1,219 whose reported record carries enough populated assessment or gauge data for this site to list and index it. At 3,200 assessed acres it ranks 939th 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 938 lakes with a larger one.
Water level
A USGS gauge tracks this lake's gage height daily, and the latest reading is 0.01 ft below the reading 30 days earlier, against a 365-day observed range of 1.4 ft.
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.
Water level: 365-day record
Daily gage height values, feet above this gauge’s own local zero, not above sea level, from USGS gauge 425715089164700 (Lake Kegonsa at Barber Drive Near Stoughton, Wi), shown weekly. Readings are daily-batch snapshots, not real-time conditions.
- Latest reading
- 3.2 ft 0.009999999999999787ft vs 30 days earlier
- 2026-08-16 · Provisional, subject to USGS revision
Water level: 365-day record
Subscribe to water level updates for Lake Kegonsa (RSS)
192 of the 309 daily values in this window (62%) are provisional and subject to USGS revision; USGS has approved this gauge's record through 2025-12-10.
Full gauge record: USGS monitoring location 425715089164700
In context
Where Lake Kegonsa 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
3,200 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
2 Longer than most more listed causes than 80% 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 Kegonsa. Hover or tap any bar for its full count and share.
In context
Wisconsin context
ATTAINS carries 19,871 lake-type waterbodies in Wisconsin, 493 assessed as not supporting at least one use and 4,225 fully supporting. Among the 1,219 indexed units there, Lake Kegonsa ranks 17th by listed-cause count (2 listed causes) and 31st by assessed size among the 1,170 with an area filed; it sits in the not-supporting set (493 statewide) . Its listed causes include Phosphorus, Total; and Perfluorooctane Sulfonate (PFOS), which also appear among Wisconsin's most-filed impairment causes (led by Phosphorus, Total).
| Other large assessed lakes in Wisconsin | Assessed acres |
|---|---|
| Lake Winnebago Not Supporting | 131,942 |
| Lake Pepin Not Supporting | 25,503 |
| Petenwell Lake Not Supporting | 23,001 |
| Lake Poygan Not Supporting | 14,024 |
| Lake Chippewa Fully Supporting | 13,616 |
| Turtle Flambeau Flowage Not Supporting | 12,943 |
Peers near Lake Kegonsa's size or cause load
Similar assessed acres
Nearest filed extents (3,200 acres here).
- Gibson Generating Plant Lake · 3,200 acres · IN
- Heron (North Heron) · 3,204 acres · MN
- Lake Erie Islands Shoreline (<=3m) · 3,194 acres · OH
- Conesus Lake · 3,208 acres · NY
Similar cause load
Nearest listed-cause counts (2 here). Peers already in the acreage column are omitted.
- 12th St. Beach · 2 causes · IL
- 31st St. Beach · 2 causes · IL
- 49th St. Beach · 2 causes · IL
- 57th St. Beach · 2 causes · IL
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
- Water levels shown are daily snapshots. Seasonal drawdown and datum conventions matter when comparing levels. How to read level data
- 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 WI10027603. 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.