waterbycounty
Federal water data

County water report

Clark County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Clark County, Wisconsin.

Water grade

F

Water score

22.0

State rank

#56

of 71

Health violations

11

EPA SDWIS, 5-year lookback

Watershed impaired

13.8%

356 water bodies assessed

Monitoring sites

33

2,367 recent measurements

Live streamflow

31%

BLACK RIVER AT NEILLSVILLE, WI

Water at a glance

Key Water Indicators for Clark County

EPA SDWIS

Safety Grade

F

Score: 22.0 / 100

EPA SDWIS

Active Violations

11

5-year health-based lookback

EPA ATTAINS

Watershed Health

14% impaired

356 bodies assessed

USGS NWIS

Streamflow Snapshot

31% of mean

BLACK RIVER AT NEILLSVILLE, WI

EPA WQP

Monitoring Sites

33

2,367 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

F

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

22.0/100

Health violations

11

Health-based violations

Violations per 100K served

109.6

Population-normalized SDWIS rate

Editorial analysis

Understanding Clark County’s Water

Drinking Water Quality Overview

EPA SDWIS

Clark County's water systems carry a failing grade, scoring 22.0 out of 100. Over the past five years, EPA SDWIS records 11 health-based violations — a pattern that public water utilities are required to disclose and correct.

Watershed Conditions

EPA ATTAINS

Under the Clean Water Act §303(d), EPA ATTAINS tracks whether waterways meet quality standards for drinking, recreation, and aquatic life (reporting cycle: 2022). A notable 13.8% of assessed waterways carry an impairment designation (49 of 356 water bodies) across Clark County's watersheds. The leading impairment causes are phosphorus, total and mercury. Impairment does not mean tap water is unsafe — it measures ambient waterway conditions upstream of treatment, not finished drinking water.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T14:00:00.000-05:00) puts BLACK RIVER at 196.0 cfs — well below its long-term average at 31% of mean — low-flow conditions worth noting for water-dependent ecosystems. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

Monitoring Network

EPA WQP

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. Clark County has moderate coverage with 33 active monitoring sites with 2,367 recent measurements on record. Predominant monitoring categories include organics, pesticide and physical. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.

Editorial advisory

What the data suggests for Clark County

Water Verdict

Clark County, Wisconsin receives a poor water quality assessment with a grade of F and a score of 22.0 out of 100. The water supply has documented quality issues. Residents are strongly encouraged to use filtered or bottled water for drinking and to stay informed about utility improvement plans. Separately, EPA ATTAINS assessments cover 356 water bodies in the county's watershed, with 13.8% listed as impaired under the Clean Water Act — a source-water measure that is tracked independently of tap-water compliance. At the most recent USGS reading, local streamflow was below its historical mean at 31.4% — worth watching in drier seasons.

Violation Context

EPA SDWIS records for Clark County, Wisconsin show 11 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 109.6 violations per 100,000 people served, this rate is high and signals significant water quality management issues. For independent context, 2,367 water-quality monitoring results have been recorded across the county in the EPA Water Quality Portal over the past five years.

Consumer Guidance

Drinking-water compliance in Clark County is rated Grade F, reflecting significant health-based violations in the recent reporting period. Clark County's drinking-water compliance score is 22.0 out of 100. An NSF 53 or NSF 58-certified filter is recommended for drinking and cooking water. Check the Consumer Confidence Report from your utility to identify the specific contaminants and required corrective actions — utilities are legally required to notify customers of violations. Phosphorus, Total is the leading impairment cause in Clark County's watershed. With 33 active water-quality monitoring sites in Clark County, data coverage is strong. A pipeline streamflow snapshot from the BLACK RIVER gauge is also available on this page.

Regional Context

Clark County has poorer water quality than the average county in Wisconsin. Its water score is 17.5 points lower than the state average, suggesting more challenges with contamination control or infrastructure than neighboring counties.

Advisory text summarizes county-level public records and is not a replacement for your utility's current Consumer Confidence Report or direct local notices.

Contaminants & Resources

Key issues flagged in Clark County's water environment

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Phosphorus (excess nutrients)

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 2

    Mercury

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 3

    Cause Unknown

    Impairment cause per EPA Clean Water Act §303(d) assessment

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Clark County

EPA How's My Waterway

Interactive watershed health data for Clark County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Clark County

Consumer Confidence Reports (WI)

Annual water quality reports from utilities in Wisconsin

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

13.8%

49 of 356 assessed

Some impairment

Top Impairment Causes

  • 1

    PHOSPHORUS, TOTAL

  • 2

    MERCURY

  • 3

    CAUSE UNKNOWN

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

33

Active in the past 5 years

Measurements Recorded

2.4K

2,367 total readings

Most Measured

  • Organics, Pesticide
  • Physical
  • Biological, Counts

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

196cfs

May 14, 7:00 PM UTC

vs Long-Term Average

31%

Well below typical

Primary Streamgage

BLACK RIVER AT NEILLSVILLE, WI

USGS site
05381000
Drainage area
749 sq mi
Long-term mean
625 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; the percent-of-typical value compares the latest reading against that average.

Free tool

Estimate Your Water Costs

Water Cost Estimate

3

3 people  ·  ~225 gal/day

Annual Total

$558

Monthly

$47

Water Bill

$558/yr

Filter Cost

$0/yr

Safety Grade for Clark County:C — Moderate

Some violations or watershed impairment detected.

Estimates use the national average residential water rate ($0.0068/gal, EPA/AWWA 2023) and EPA WaterSense per-person consumption baseline (75 gal/person/day). Actual bills vary by utility, usage tier, and local infrastructure fees. For informational purposes only.

Try the full calculator →

Improve your water quality at home

Berkey filters remove 99.9%+ of contaminants from tap water.

Shop Berkey →

Sponsored

Test your tap water

Tap Score provides professional mail-in water testing.

Get Tested →

Frequently Asked Questions

What is the water quality in Clark County, Wisconsin?
Clark County, Wisconsin has a drinking-water quality grade of F with a score of 22.0/100, based on EPA SDWIS compliance data. The county has 11 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and streamflow snapshots are reported separately on this page.
Are there any water violations in Clark County?
Clark County has 11 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 Clark County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 13.8% of Clark County's 356 assessed water bodies are classified as impaired (49 impaired). The top reported causes are PHOSPHORUS, TOTAL, MERCURY, CAUSE UNKNOWN. 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 Clark County?
EPA's Water Quality Portal records 2,367 measurements from 33 monitoring sites in Clark County over the past five years. The most frequently measured characteristic groups are Organics, Pesticide, Physical, Biological, Counts. 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 Clark County right now?
Clark County's primary USGS streamgage on the BLACK RIVER has a pipeline snapshot of 196 cubic feet per second — 31% of the long-term mean of 625.18 cfs. This is well below typical — often a signal of drought stress on source water. For the latest gauge feed, visit waterdata.usgs.gov.
How does Clark County water compare to the Wisconsin average?
Clark County's SDWIS water quality score of 22.0/100 is lower 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 Clark County?
Based on EPA SDWIS data, Clark County has a water quality grade of F (22.0/100). 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 Clark County have so many water violations?
Clark County has 11 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 Clark County rank for water quality in Wisconsin?
Clark County ranks #56 out of 71 counties in Wisconsin by SDWIS water quality score (1 = best). With a score of 22.0/100, it falls in the bottom 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

Vernon County

Wisconsin

F

22.0

Water score

Columbia County

Wisconsin

F

22.3

Water score

Crawford County

Wisconsin

F

21.1

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 and 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 Evan Brooks, Data EditorUpdated Reviewed by Evan Brooks, Data Editor

Explore more data for Clark County

Property TaxCost of LivingCrime RateIncomeHealthSchoolsDisaster RiskWeatherCounty Score