Deep Lake
Lake County, IllinoisView mapDirections
Illinois EPA publishes the water-quality measurements for Deep Lake. Here is what has been measured.
- Mesotrophic
- Impaired · Mercury
- 38 ft max depth
- Limited data
Deep Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Chlorophyll-a (algae): 2.2 µg/L.
Deep Lake is a mesotrophic lake in Lake County, Illinois with an estimated average depth of about 38 feet. Compared to the 18 other monitored lakes in Lake County, Deep Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2022-08-10. Methodology: how these readings are compared.
Swimming conditions
Readings onlyBacteria advisory
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. Deep Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pathogens (E. coli, fecal). Check local advisories before you swim.
Whether Deep 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 Deep Lake
These are the measurements Illinois EPA publishes for Deep Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Chlorophyll-a 2.2 µg/L. TSI 38.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | 2.2µg/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. | 38 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Deep Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~38 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 Deep Lake.
Lake Size & Watershed
Watershed (drainage) area
8 sq mi
HydroLAKES / HydroSHEDS
Surface area
208 acres
HydroLAKES / HydroSHEDS
Shoreline
2.7 mi
HydroLAKES / HydroSHEDS
Elevation
778 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.
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Stays near Deep Lake
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Fishing Deep Lake
EPA Impairment Status
Deep Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Fish consumption, Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_VTD · Official waterbody report
Nearby Lakes in Lake County
Frequently asked questions about Deep Lake
Where is Deep Lake?
- Deep 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 Deep Lake?
- Deep Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Chlorophyll-a (algae): 2.2 µg/L.
Is Deep Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Deep Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pathogens (E. coli, fecal). Check local advisories before you swim.
How deep is Deep Lake?
- No published bathymetric survey covers Deep Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 38 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
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Where this data comes from
8 measurements from 1 monitoring station, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX8 samples · 2022
Analytical methods
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (1)
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)