Opeka Lake is a productive, nutrient-rich eutrophic lake in Cook County, Illinois. Water quality is graded B based on 2 sampling years through 2020. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 67 other monitored lakes in Cook County, Opeka Lake ranks #8 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2020-10-06. Grade methodology: LakeGrade methodology.
Watch Opeka Lake water quality
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B, Good
Murky, only visible to about 3.9 ft. Phosphorus level: 15.5 µg/L. Trophic State Index: 51.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.9 ft | D |
| Phosphorus | 15.5 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Opeka Lake
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Fishing Opeka Lake
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -21.5 m/yr | 2 |
Recreation & Access
Water Temperature
Opeka Lake averages about 79°F at the surface in summer, usually warmest in Jul (about 82°F) and coldest in Oct (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 42 field readings (2020–2020) via the EPA Water Quality Portal. See the full Opeka Lake water temperature breakdown →
Location
County Ranking
Ranked #8 of 68 lakes in Cook County
Cleaner Lakes Within 30 Miles
Opeka Lake holds Grade B. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Cook County
Explore Opeka Lake across LakeGrade
More Illinois Lake Rankings
Other Grade B Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
EPA Impairment Status
Opeka Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit IL_RGF · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Opeka Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Canadian Pacific-Bensenville Rail YardFranklin Park · 4.9 mi away · NPDES IL0002151Recent 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)
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: 2020-10-06
Monitoring stations: 3