Grays Lake is a productive, nutrient-rich eutrophic lake in Lake County, Illinois. Water quality is graded B based on 2 sampling years through 2021. Public access is available with 2 public boat landings. Compared to the 15 other monitored lakes in Lake County, Grays Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2021-10-12. Grade methodology: LakeGrade methodology.
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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 3.5 ft. Phosphorus level: 18 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.5 ft | D |
| Phosphorus | 18 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Grays Lake
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Fishing Grays Lake
Recreation & Access
Water Temperature
Grays Lake averages about 73°F at the surface in summer, usually warmest in Jul (about 80°F) and coldest in May (about 64°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 54 field readings (2018–2021) via the EPA Water Quality Portal. See the full Grays Lake water temperature breakdown →
Location
County Ranking
Ranked #5 of 16 lakes in Lake County
Cleaner Lakes Within 30 Miles
Grays Lake holds Grade B. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Lake County
Explore Grays 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 B Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
EPA Impairment Status
Grays 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_UTL · Official waterbody report · Matched by proximity (2.22 km)
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 Grays Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Countryside LandfillGrayslake · 1.1 mi away · NPDES IL0075558Recent 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: 2021-10-12
Monitoring stations: 3