Big Rock Lake is a mesotrophic lake in Kane County, Illinois. Water quality is graded B based on 2 sampling years through 2022.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2022-10-11. Grade methodology: LakeGrade methodology.
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B, Good
Moderate clarity, visible to about 8.1 ft. Phosphorus level: 10 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.1 ft | C |
| Phosphorus | 10 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Big Rock Lake
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Fishing Big Rock Lake
Water Temperature
Big Rock Lake averages about 57°F at the surface in summer, usually warmest in Aug (about 58°F) and coldest in May (about 51°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 231 field readings (2022–2022) via the EPA Water Quality Portal. See the full Big Rock Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 1 lakes in Kane County
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Mesotrophic Lakes in Illinois
More records, surveys & data sources
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Big Rock Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Big Rock Stp, Village OfBig Rock · 2.2 mi away · NPDES IL0079464Recent 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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-10-11
Monitoring stations: 2