Coulterville Lake is a highly nutrient-loaded hypereutrophic lake in Randolph County, Illinois. 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, Illinois DNR, last sampled 2022-10-18. Grade methodology: LakeGrade methodology.
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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
Where to stay near Coulterville Lake
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Fishing Coulterville Lake
Water Temperature
Coulterville Lake averages about 84°F at the surface in summer, usually warmest in Jul (about 86°F) and coldest in Oct (about 60°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 260 field readings (2012–2022) via the EPA Water Quality Portal. See the full Coulterville Lake water temperature breakdown →
Location
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.
- BBoulder South LakePerry County · 16 mi · Two grade letters higher (F → B)
- DSparta Northwest LakeRandolph County · 7.1 mi · Higher grade (F → D)
- DRandolph LakeRandolph County · 18.4 mi · Higher grade (F → D)
- DWesslyn Cut LakePerry County · 16.1 mi · Higher grade (F → D)
Nearby Lakes in Randolph County
Explore Coulterville Lake across LakeGrade
Species activity outlook by water temperature and season
Where to stay at Illinois's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
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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
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_ROV · Official waterbody report
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Coulterville Lake under Clean Water Act (NPDES) discharge permits. 3 facilities have a reported Clean Water Act violation in the past three years.
- Peabody Gateway North Mining LlcCoulterville · 1.2 mi away · NPDES IL0079481Recent violation
- Peabody Coulterville Mining LlcCoulterville · 2.9 mi away · NPDES IL0062189Recent violation
- Prairie State Generating Company LlcMarissa · 4.7 mi away · NPDES IL0077526Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-10-18
Monitoring stations: 3