Grays Lake
Lake County, IllinoisView mapDirections
Illinois EPA publishes the water-quality measurements for Grays Lake. Here is what has been measured.
- Mesotrophic
- 48 ft max depth
- Limited data
Grays Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 3.5 ft visibility. Phosphorus: 23 µg/L. Chlorophyll-a (algae): 3.1 µg/L.
Grays Lake is a mesotrophic lake in Lake County, Illinois with an estimated average depth of about 48 feet. Compared to the 18 other monitored lakes in Lake County, Grays Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2021-10-12. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Grays Lake is safe to swim in today is a call for the Illinois Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Grays Lake
These are the measurements Illinois EPA publishes for Grays Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 3.5 ft. Phosphorus 23 µg/L. Chlorophyll-a 3.1 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 3.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 23µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 3.1µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 50 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Grays Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Grays Lake typically sits around 67°F at the surface in October. Summer average is about 73°F. Usually warmest in Jul (about 80°F) and coldest in May (about 64°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (64°F) to its warmest (80°F).
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 →
Lake Details
Max depth
~48 ft est.
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Grays Lake.
Lake Size & Watershed
Watershed (drainage) area
0 sq mi
HydroLAKES / HydroSHEDS
Surface area
67 acres
HydroLAKES / HydroSHEDS
Shoreline
1.4 mi
HydroLAKES / HydroSHEDS
Elevation
784 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Stays via Stay22
Stays near Grays Lake
Compare lakeside cabins, hotels, and vacation rentals near Grays Lake in Lake County, Illinois — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Grays Lake
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Fishing Grays Lake
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.
Nearby Lakes in Lake County
Frequently asked questions about Grays Lake
Where is Grays Lake?
- Grays Lake is a lake in Lake County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Grays Lake?
- Grays Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 3.5 ft visibility. Phosphorus: 23 µg/L. Chlorophyll-a (algae): 3.1 µg/L.
Is Grays Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Grays Lake?
- Grays Lake typically sits around 67°F at the surface in October, from 54 EPA Water Quality Portal field readings (2018–2021). That is a typical value for the month, not a live reading.
How deep is Grays Lake?
- No published bathymetric survey covers Grays Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 48 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Grays Lake across LakeQuality
Species activity outlook by water temperature and season
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Where to stay at Illinois's top lakes, each with its readings
Illinois's cleanest lakes, ranked on agency measurements
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Other Lakes in Illinois
Mesotrophic Lakes in Illinois
Where this data comes from
50 measurements from 3 monitoring stations, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX50 samples · 2021
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (3)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)