Carlyle Lake
Clinton County, Illinois24,580 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Mercury
- #1 of 1 in the county
- 53 ft max depth
- Public access
- Limited data
Carlyle Lake in Clinton County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1.8 ft visibility. Phosphorus: 238.5 µg/L. Chlorophyll-a (algae): 38.8 µg/L. Surface area: 24580 acres.
- Clarity
- 1.8 ft
- Max depth
- ~53 ft est.
- Area
- 24,580 acres
- Type
- Hypereutrophic
- Phosphorus
- 238.5 µg/L
- Chlorophyll-a
- 38.8 µg/L
- Public access
- Yes
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Carlyle Lake is a 24,580-acre highly nutrient-loaded hypereutrophic lake in Clinton County, Illinois with an estimated average depth of about 53 feet. Water quality is graded F based on 2 sampling years through 2021. Limited fish-species data available. Public access is available with 14 public boat landings.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2021-11-03. Grade methodology: LakeQuality methodology.
What Carlyle Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch14 documented ramps
- Big water24,580 acres
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The F is nutrients and algae, not a swimming clearance. Carlyle Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.8 ft of visibility. Phosphorus 238.5 µg/L. Chlorophyll-a 38.8 µg/L. TSI 73. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.8 ft | Not graded |
| Phosphorus | 238.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 38.8 µg/L | Poor |
| Trophic State Index (TSI) | 73 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~53 ft est. |
| Average Depth | ~19 ft est. |
| Surface Area | 24,580 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Carlyle Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Boulder Access MarinaPublic
- Carlyle LakePublic
- Carlyle LakePublic
- Carlyle LakePublic
- Carlyle LakePublic
- Carlyle LakePublic
Showing 6 of 14 documented landings from the USGS National Boat Ramps inventory.
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Carlyle Lake
Reservoir Info (USACE NID)
Carlyle Lake is a man-made reservoir impounded by the Carlyle Dam - Keyesport Levee (completed 1966), built primarily for flood risk reduction on the KASKASKIA RIVER; earth-type dam, 23 ft tall and 9,945 ft long.
- Surface area
- 24,580 ac
- Normal storage
- 233,000 ac-ft
- Max storage
- 1,286,900 ac-ft
- Drainage area
- 0.9 sq mi
- Hazard class
- High
- Owner
- USACE - St. Louis District
All listed purposes: Flood Risk Reduction;Other;Navigation;Fish and Wildlife Pond;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IL00113 · Operator website
EPA Impairment Status
Carlyle Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_ROA · Official waterbody report
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Carlyle Lake under Clean Water Act (NPDES) discharge permits. 3 facilities have a reported Clean Water Act violation in the past three years.
- Department Of The ArmyCarlyle · 2.2 mi away · NPDES IL0025933Recent violation
- Hickory Shores Resort - StpCarlyle · 3.2 mi away · NPDES IL0061697Recent violation
- Eldon Hazlet State Park Campground StpCarlyle · 3.5 mi away · NPDES IL0053996Recent 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.
County Ranking
Ranked #1 of 1 lakes in Clinton County
Nearby Lakes in Clinton County
Frequently asked questions about Carlyle Lake
Where is Carlyle Lake?
- Carlyle Lake is a lake in Clinton County, Illinois. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Carlyle Lake?
- Carlyle Lake in Clinton County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1.8 ft visibility. Phosphorus: 238.5 µg/L. Chlorophyll-a (algae): 38.8 µg/L. Surface area: 24580 acres.
Is Carlyle Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Carlyle Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
How deep is Carlyle Lake?
- No published bathymetric survey covers Carlyle Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 53 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 24580 acres.
Are there boat ramps on Carlyle Lake?
- Carlyle Lake has 14 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Boulder Access Marina, Carlyle Lake, Carlyle Lake, Carlyle Lake, among others. Public access is listed as yes.
Explore Carlyle Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
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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Where this data comes from
93 measurements from 5 monitoring stations, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX93 samples · 2021
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (5)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory