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EPA SDWIS

Lemhi County Water Quality

Lemhi County, Idaho

Water Grade

F

Water Score

9.2

Violations

13

State Rank

#36

of 44 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

F

Based on EPA compliance history and violation data

Water Score

9.2/100

Higher = better quality

Health Violations

13

Health-based violations

Violation Rate

367.8%

Systems with violations

Water Advisory: Lemhi County

Water Verdict

Lemhi County receives a poor water quality assessment with a grade of F and a score of 9.2 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.

Violation Context

Lemhi County has recorded 13 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 367.8 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Residents of Lemhi 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 13 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

Lemhi County has poorer water quality than the average county in Idaho. Its water score is 23.4 points lower than the state average, suggesting more challenges with contamination control or infrastructure than neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

25.1%

210 of 838 assessed

Some impairment

Top Impairment Causes

  • 1

    TEMPERATURE

  • 2

    SEDIMENTATION/SILTATION

  • 3

    FLOW REGIME MODIFICATION

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

79

Active in the past 5 years

Measurements Recorded

4.2K

4,206 total readings

Most Measured

  • Biological, Counts
  • Biological, Fish
  • Physical

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

8,120cfs

May 14, 6:30 PM UTC

vs Long-Term Average

281%

Well above typical

Primary Streamgage

SALMON RIVER NR SHOUP ID

USGS site
13307000
Drainage area
6,239 sq mi
Long-term mean
2,886 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 Lemhi County, Idaho?
Lemhi County, Idaho has a drinking-water quality grade of F with a score of 9.2/100, based on EPA SDWIS compliance data. The county has 13 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 Lemhi County?
Lemhi County has 13 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 Lemhi County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 25.1% of Lemhi County's 838 assessed water bodies are classified as impaired (210 impaired). The top reported causes are TEMPERATURE, SEDIMENTATION/SILTATION, FLOW REGIME MODIFICATION. 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 Lemhi County?
EPA's Water Quality Portal records 4,206 measurements from 79 monitoring sites in Lemhi County over the past five years. The most frequently measured characteristic groups are Biological, Counts, Biological, Fish, Physical. 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 Lemhi County right now?
Lemhi County's primary USGS streamgage on the SALMON RIVER is currently reading 8,120 cubic feet per second — 281% of the long-term mean of 2,885.52 cfs. This is well above typical — often a signal of recent precipitation or storm runoff. For genuine real-time data, visit waterdata.usgs.gov.
How does Lemhi County water compare to the Idaho average?
Lemhi County's SDWIS water quality score of 9.2/100 is lower than the Idaho state average of 32.6. The average water quality grade across Idaho is F, based on data from 44 counties with available SDWIS data.
Is tap water safe to drink in Lemhi County?
Based on EPA SDWIS data, Lemhi County has a water quality grade of F (9.2/100). 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 Lemhi County have so many water violations?
Lemhi County has 13 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 Lemhi County rank for water quality in Idaho?
Lemhi County ranks #36 out of 44 counties in Idaho by SDWIS water quality score (1 = best). With a score of 9.2/100, 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

Lewis County

Idaho

F

9.1

Water score

Clark County

Idaho

F

8.7

Water score

Franklin County

Idaho

F

8.0

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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