Timber Lake is a mesotrophic lake in Lake County, Illinois. Water quality is graded B based on 1 sampling years through 2020. Limited fish-species data available. Public access is available with 8 public boat landings. Compared to the 15 other monitored lakes in Lake County, Timber Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2020-07-20. 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 10.6 ft. Trophic State Index: 43.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.6 ft | B |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Timber Lake
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Fishing Timber Lake
Recreation & Access
Location
County Ranking
Ranked #3 of 16 lakes in Lake County
Nearby Lakes in Lake County
Explore Timber Lake across LakeGrade
Species activity outlook by water temperature and season
Top lakes and where to stay in the Chain O'Lakes area
Where to stay at Illinois's top lakes, each with its grade
Moderate nutrients, good water quality
Illinois's cleanest and most-polluted lakes, ranked
More Illinois Lake Rankings
Other Grade B Lakes in Illinois
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 1949), built primarily for recreation on the TRIB TOWER LAKE; earth-type dam, 20 ft tall and 320 ft long.
- Normal storage
- 240 ac-ft
- Max storage
- 292 ac-ft
- Hazard class
- Low
- Owner
- MICHAEL GRAFF
Source: USACE National Inventory of Dams, NID ID IL00632 · Operator website
EPA Impairment Status
Timber 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_RTZQ · Official waterbody report · Matched by proximity (0.04 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
5 EPA-permitted facilities operate within about 5 miles of Timber Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 4 facilities have a reported Clean Water Act violation in the past three years.
- Wauconda WwtfWauconda · 1.7 mi away · NPDES IL0020109MajorRecent violation
- Mount Saint Joseph Home StpLake Zurich · 1.1 mi away · NPDES IL0027286Recent violation
- North Barrington Elementary School StpBarrington · 2 mi away · NPDES IL0024716Recent violation
- Lake Barrington Homeowners Association StpLake Barrington · 2.9 mi away · NPDES IL0045110Recent violation
- Cm Products IncLake Zurich · 4.3 mi away · NPDES IL0066311
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: 2020-07-20
Monitoring stations: 1