Randolph Lake is a productive, nutrient-rich eutrophic lake in Randolph County, Illinois. Water quality is graded D based on 2 sampling years through 2021. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 2 other monitored lakes in Randolph County, Randolph Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2021-10-13. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 1.7 ft of visibility. Phosphorus level: 49 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.7 ft | F |
| Phosphorus | 49 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Randolph Lake
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Fishing Randolph Lake
Recreation & Access
Water Temperature
Randolph Lake averages about 71°F at the surface in summer, usually warmest in Jul (about 73°F) and coldest in May (about 61°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 257 field readings (2016–2021) via the EPA Water Quality Portal. See the full Randolph Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 3 lakes in Randolph County
Cleaner Lakes Within 30 Miles
Randolph Lake holds Grade D. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Randolph County
Explore Randolph Lake across LakeGrade
More Illinois Lake Rankings
Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
Reservoir Info (USACE NID)
Randolph Lake is a man-made reservoir impounded by the Randolph County Lake Dam (completed 1960), built primarily for recreation on the MORRISON BRANCH; earth-type dam, 47 ft tall and 665 ft long.
- Normal storage
- 946 ac-ft
- Max storage
- 1,563 ac-ft
- Hazard class
- Significant
- Owner
- ILLINOIS DEPARTMENT OF NATURAL RESOURCES
Source: USACE National Inventory of Dams, NID ID IL00551 · Operator website · Matched by proximity (0.44 km)
EPA Impairment Status
Randolph 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_RIB · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2021-10-13
Monitoring stations: 3