Coulterville Lake
Randolph County, IllinoisView mapDirections
Illinois EPA publishes the water-quality measurements for Coulterville Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- Limited data
Coulterville Lake in Randolph County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 2.7 ft visibility. Phosphorus: 452.5 µg/L. Chlorophyll-a (algae): 51 µg/L.
Coulterville Lake is a highly nutrient-loaded hypereutrophic lake in Randolph County, Illinois. 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 EPA, last sampled 2022-10-18. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Coulterville Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Coulterville Lake is safe to swim in today is a call for the Illinois Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Coulterville Lake
These are the measurements Illinois EPA publishes for Coulterville Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 2.7 ft of visibility. Phosphorus 452.5 µg/L. Chlorophyll-a 51 µg/L. TSI 75.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 2.7ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 453µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 51µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 75 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Coulterville Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Coulterville Lake typically sits around 60°F at the surface in October. Summer average is about 84°F. Usually warmest in Jul (about 86°F) and coldest in Oct (about 60°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (60°F) to its warmest (86°F).
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 →
Stays via Stay22
Stays near Coulterville Lake
Compare lakeside cabins, hotels, and vacation rentals near Coulterville Lake in Randolph County, Illinois — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Coulterville Lake are listed below.
Top-rated places to stay near Coulterville Lake
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Fishing Coulterville 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
Designated uses not supporting: Other.
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.
Nearby Lakes in Randolph County
Frequently asked questions about Coulterville Lake
Where is Coulterville Lake?
- Coulterville Lake is a lake in Randolph County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Coulterville Lake?
- Coulterville Lake in Randolph County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 2.7 ft visibility. Phosphorus: 452.5 µg/L. Chlorophyll-a (algae): 51 µg/L.
Is Coulterville Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Coulterville Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Coulterville Lake?
- Coulterville Lake typically sits around 60°F at the surface in October, from 260 EPA Water Quality Portal field readings (2012–2022). That is a typical value for the month, not a live reading.
Explore Coulterville Lake across LakeQuality
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Other Lakes in Illinois
Hypereutrophic Lakes in Illinois
Where this data comes from
49 measurements from 3 monitoring stations, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX49 samples · 2022
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (3)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)