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EPA SDWIS

Winnebago County Water Quality

Winnebago County, Wisconsin

Water Grade

D

Water Score

47.9

Violations

28

State Rank

#23

of 71 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

D

Based on EPA compliance history and violation data

Water Score

47.9/100

Higher = better quality

Health Violations

28

Health-based violations

Violation Rate

19.3%

Systems with violations

Water Advisory: Winnebago County

Water Verdict

Winnebago County receives a below-average water quality assessment with a grade of D and a score of 47.9 out of 100. Residents should review their utility's Consumer Confidence Report and may want to consider additional water filtration for drinking.

Violation Context

Winnebago County has recorded 28 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 19.3 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Residents of Winnebago County are advised to use filtered or bottled water for drinking and cooking until water quality improves. A reverse-osmosis or activated-carbon filter certified to remove the contaminants listed in the utility's Consumer Confidence Report is recommended. With 28 recorded health violations, staying informed about utility communications and boil-water notices is especially important. For long-term peace of mind, request your utility's latest Consumer Confidence Report and consider independent water testing if you have specific health concerns.

Regional Context

Winnebago County has better water quality than the average county in Wisconsin. Its water score is 8.4 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

12.3%

24 of 195 assessed

Some impairment

Top Impairment Causes

  • 1

    PHOSPHORUS, TOTAL

  • 2

    TOTAL SUSPENDED SOLIDS (TSS)

  • 3

    POLYCHLORINATED BIPHENYLS (PCBS)

Source: EPA ATTAINS · Reporting cycle 2022

Impairment is determined under the Clean Water Act §303(d): a water body is impaired when it fails to meet state-defined quality standards for designated uses (drinking, recreation, aquatic life). Assessment coverage varies by state — counties without assessed water bodies are not shown.

Past 5 years

Water Quality Monitoring

Monitoring Sites

36

Active in the past 5 years

Measurements Recorded

24K

23,695 total readings

Most Measured

  • Physical
  • Nutrient
  • Organics, Pesticide

Categories measured most frequently

Data from the EPA Water Quality Portal (WQP), aggregating monitoring records from federal, state, and tribal sources. Each measurement represents a single sample analyzed for a specific characteristic (e.g., E. coli, pH, dissolved oxygen, nitrogen).

Live USGS Streamgage

River & Stream Conditions

Current Discharge

3,050cfs

May 14, 7:00 PM UTC

vs Long-Term Average

65%

Below typical

Primary Streamgage

FOX RIVER AT OSHKOSH, WI

USGS site
04082400
Drainage area
5,310 sq mi
Long-term mean
4,687 cfs

One representative streamgage (the one with the largest drainage area in the county). Many counties have multiple gauges — this view summarizes the primary one. The long-term mean is the full-record annual average; "% of typical" compares the latest reading against that average.

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Frequently Asked Questions

What is the water quality in Winnebago County, Wisconsin?
Winnebago County, Wisconsin has a drinking-water quality grade of D with a score of 47.9/100, based on EPA SDWIS compliance data. The county has 28 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in Winnebago County?
Winnebago County has 28 health-based drinking water violations recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Violations may have been resolved — check with your local water utility for current status.
How healthy are the watersheds in Winnebago County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 12.3% of Winnebago County's 195 assessed water bodies are classified as impaired (24 impaired). The top reported causes are PHOSPHORUS, TOTAL, TOTAL SUSPENDED SOLIDS (TSS), POLYCHLORINATED BIPHENYLS (PCBS). Impairment means the water body fails to meet state quality standards for at least one designated use — drinking water source, recreation, aquatic life, or fish consumption. Note: watershed impairment doesn't always translate to tap-water issues; treatment plants can remove most regulated contaminants.
How much water-quality monitoring happens in Winnebago County?
EPA's Water Quality Portal records 23,695 measurements from 36 monitoring sites in Winnebago County over the past five years. The most frequently measured characteristic groups are Physical, Nutrient, Organics, Pesticide. Each measurement is a single sample analyzed for one characteristic (E. coli, pH, dissolved oxygen, etc.). High monitoring density means more scientific evidence behind any reported signal — it does not by itself indicate water quality.
What's happening with rivers in Winnebago County right now?
Winnebago County's primary USGS streamgage on the FOX RIVER is currently reading 3,050 cubic feet per second — 65% of the long-term mean of 4,687.45 cfs. Flow is within typical range for this gauge. For genuine real-time data, visit waterdata.usgs.gov.
How does Winnebago County water compare to the Wisconsin average?
Winnebago County's SDWIS water quality score of 47.9/100 is higher than the Wisconsin state average of 39.5. The average water quality grade across Wisconsin is F, based on data from 71 counties with available SDWIS data.
Is tap water safe to drink in Winnebago County?
Based on EPA SDWIS data, Winnebago County has a water quality grade of D (47.9/100). This indicates below-average compliance with significant violations. Residents may want to consider home water filtration or independent testing. The grade speaks to the public water system, not the watershed — for watershed-level concerns, see the Watershed Health zone. For the most up-to-date information, contact your local water utility or review your Consumer Confidence Report (CCR).
Why does Winnebago County have so many water violations?
Winnebago County has 28 health-based drinking water violations on record from the EPA SDWIS database. A higher violation count can result from aging infrastructure, underfunded water utilities, agricultural runoff contamination, or industrial pollution. Counties with more water systems may also see more violations simply due to scale. Residents concerned about water quality should consider independent water testing and home filtration systems.
How does Winnebago County rank for water quality in Wisconsin?
Winnebago County ranks #23 out of 71 counties in Wisconsin by SDWIS water quality score (1 = best). With a score of 47.9/100, it falls in the top third of counties statewide. The ranking reflects EPA SDWIS compliance only — not watershed impairment, monitoring density, or streamflow, which are tracked separately on this page.

Counties with Similar Water Quality

Dunn County

Wisconsin

D

48.2

Water score

Pierce County

Wisconsin

D

48.2

Water score

Kenosha County

Wisconsin

D

49.0

Water score

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.

Watershed health and impaired-waterway data from the EPA ATTAINS Clean Water Act §303(d) assessments — state-reported, EPA-finalized.

Water-quality monitoring counts from the EPA Water Quality Portal (WQP) — federated USGS, EPA, and state agency sampling records over a rolling 5-year window.

Live streamflow from the USGS National Water Information System (NWIS) — continuous discharge measurements from the largest-drainage gauge in each county, compared against the full-record long-term annual mean.

Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.

By Logan Johnson, Founder & Data EditorUpdated Reviewed by Logan Johnson, Founder & Data Editor

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