Grass Lake is a productive, nutrient-rich eutrophic lake in Lake County, Illinois. Water quality is graded D based on 2 sampling years through 2022. Limited fish-species data available. Public access is available with 5 public boat landings. Compared to the 15 other monitored lakes in Lake County, Grass Lake ranks #10 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2022-10-26. 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 1.4 ft of visibility. Phosphorus level: 57.5 µg/L. Trophic State Index: 67.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.4 ft | F |
| Phosphorus | 57.5 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 67 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Grass Lake
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Fishing Grass Lake
Recreation & Access
Location
County Ranking
Ranked #10 of 16 lakes in Lake County
Cleaner Lakes Within 30 Miles
Grass Lake holds Grade D. 2 nearby lakes hold higher grades.
- BCatherine LakeLake County · 3.8 mi · Two grade letters higher (D → B)
- CChannel LakeLake County · 3.1 mi · Higher grade (D → C)
Nearby Lakes in Lake County
Explore Grass 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
High nutrients, frequent algae, reduced clarity
Illinois's cleanest and most-polluted lakes, ranked
More Illinois Lake Rankings
Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
EPA Impairment Status
Grass 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_RTQ · 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 Grass Lake under Clean Water Act (NPDES) discharge permits.
- Fox Lake Grade School Dist 114Spring Grove · 1.3 mi away · NPDES IL0076597
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: 2022-10-26
Monitoring stations: 2