What is the water quality grade for Coulterville Lake?

Coulterville Lake in Randolph County, Wisconsin received a water quality grade of F (Very Poor). Water clarity: 2.7 ft visibility. Phosphorus: 426 µg/L.

Is Coulterville Lake safe to swim in?

Avoid swimming, very poor water quality, potential algae toxins. Coulterville Lake has an overall water quality grade of F. Always check local health department advisories before swimming.

Coulterville Lake

Randolph County, WisconsinHypereutrophic

Coulterville Lake is a highly nutrient-loaded hypereutrophic lake in Randolph County, IL. Water quality is graded F based on 2 sampling years through 2022. Compared to the 2 other monitored lakes in Randolph County, Coulterville Lake ranks #3 for water quality.

Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2022-10-18. Grade methodology: LakeGrade methodology.

Swimming Safety

Avoid swimming, very poor water quality, potential algae toxins

Water Quality Grade: F, Very Poor

Very murky, less than 2.7 ft of visibility. Phosphorus level: 426 µg/L. Trophic State Index: 77.

Metric	Value	Grade
Water Clarity (Secchi Depth)	2.7 ft	F
Phosphorus	426 µg/L	F
Chlorophyll-a (Algae)	No data
Trophic State Index (TSI)	77	Hypereutrophic

Very high nutrients, dense algae, poor clarity

Location

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County Ranking

Ranked #3 of 3 lakes in Randolph County

Cleaner Lakes Within 30 Miles

Coulterville Lake holds Grade F. 4 nearby lakes hold higher grades.

See full comparison →

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Top 25 by overall water quality score

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Grade A/B + low algae filter

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Panfish-rich, public access

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Other Grade F Lakes in Wisconsin

Lake Charlemagne

Cook County · Clarity: 2 ft

Bode Lake North

Cook County · Clarity: 1.5 ft

Great Lakes Quarries West

Cook County · Clarity: 2.5 ft

Bull Frog Lake

Cook County · Clarity: 3 ft

Belly Deep Slough Lake

Cook County · Clarity: 0.7 ft

Sauk Lake

Cook County · Clarity: 1 ft

Hypereutrophic Lakes in Wisconsin

Bode Lake North Belly Deep Slough Lake Sauk Lake Washington Park Lagoon Lake

Reservoir Info (USACE NID)

Coulterville Lake is a man-made reservoir impounded by the Lake Coulterville Dam (completed 1917), built primarily for recreation on the TRIB SOUTH FORK MUD CREEK; earth-type dam, 18 ft tall and 460 ft long.

Normal storage: 109 ac-ft
Max storage: 181 ac-ft
Hazard class: Low
Owner: LINCOLN TRAIL BANK & TRUST COMPANY

Source: USACE National Inventory of Dams, NID ID IL00561 · Operator website

EPA Impairment Status

Coulterville Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).

Causes of impairment

Nutrients (phosphorus, nitrogen)

A Total Maximum Daily Load (TMDL) plan has been approved.

Source: EPA ATTAINS assessment unit IL_ROV · Official waterbody report

Data Sources

Water quality data from the EPA Water Quality Portal

Impairment status from EPA ATTAINS 303(d) database

Grading methodology based on Metropolitan Council standards

Most recent sample: 2022-10-18

Monitoring stations: 3