Timber Lake is a mesotrophic lake in Carroll County, Illinois. Water quality is graded B based on 1 sampling years through 2021.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2021-07-26. Grade methodology: LakeGrade methodology.
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B, Good
Good clarity, visible to about 11.5 ft. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.5 ft | B |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Timber Lake
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Fishing Timber Lake
Location
County Ranking
Ranked #1 of 1 lakes in Carroll County
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Explore Timber Lake across LakeGrade
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Mesotrophic Lakes in Illinois
More records, surveys & data sources
Reservoir Info (USACE NID)
Timber Lake is a man-made reservoir impounded by the Timber Lake Dam (completed 1960), built primarily for recreation on the TRIB EAST JOHNSON CREEK; earth-type dam, 25 ft tall and 466 ft long.
- Normal storage
- 87 ac-ft
- Max storage
- 155 ac-ft
- Hazard class
- Significant
- Owner
- TIMBER LAKE CAMPGROUND
Source: USACE National Inventory of Dams, NID ID IL00841 · Operator website
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Timber Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Mount Carroll Stp, City OfMount Carroll · 3.8 mi away · NPDES IL0020176Recent violation
- Harvel WtpHarvel · 3.5 mi away · NPDES IL0005029
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: 2021-07-26
Monitoring stations: 1