Petite Lake
Lake County, IllinoisView mapDirections
Not enough samples to grade — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. No letter yet. Here is what we do have.
- Impaired · Mercury
- 34 ft max depth
- Limited data
Petite Lake in Lake County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 2.5 ft visibility. Phosphorus: 70 µg/L. Chlorophyll-a (algae): 59 µg/L.
- Clarity
- 2.5 ft
- Typical in August
- 74°F
- Max depth
- ~34 ft est.
- Phosphorus
- 70 µg/L
- Chlorophyll-a
- 59 µg/L
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Stays near Petite Lake
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Watch Petite Lake’s letter
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Why Petite Lake has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Petite Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by Illinois EPA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Petite Lake is a lake in Lake County, Illinois with an estimated average depth of about 34 feet.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2022-10-26. Grade methodology: LakeQuality methodology.
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Petite Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pCBs. Check local advisories before you swim.
Water quality measurements for Petite Lake
These readings exist but are not enough for an A–F grade — see why.
Very murky, less than 2.5 ft of visibility. Phosphorus 70 µg/L. Chlorophyll-a 59 µg/L. TSI 67.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | Not graded |
| Phosphorus | 70 µg/L | Not graded |
| Chlorophyll-a (Algae) | 59 µg/L | Not graded |
| Trophic State Index (TSI) | 67 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Petite Lake typically sits around 74°F at the surface in August. Summer average is about 78°F. Usually warmest in Jul (about 81°F) and coldest in Oct (about 57°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 113 field readings (2012–2022) via the EPA Water Quality Portal. See the full Petite Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~34 ft est. |
| Average Depth | ~14 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 Petite Lake.
Lake Size & Watershed
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.
Fishing Petite Lake
EPA Impairment Status
Petite 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_VTW · Official waterbody report
Graded lakes near Petite Lake
Petite Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Lake County
Frequently asked questions about Petite Lake
Where is Petite Lake?
- Petite Lake is a lake in Lake County, Illinois. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Petite Lake?
- Petite Lake in Lake County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 2.5 ft visibility. Phosphorus: 70 µg/L. Chlorophyll-a (algae): 59 µg/L.
Is Petite Lake safe to swim in?
- The letter is not a swimming clearance. Petite Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pCBs. Check local advisories before you swim.
What is the water temperature of Petite Lake?
- Petite Lake typically sits around 74°F at the surface in August, from 113 EPA Water Quality Portal field readings (2012–2022). That is a typical value for the month, not a live reading.
How deep is Petite Lake?
- No published bathymetric survey covers Petite Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 34 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Petite Lake across LakeQuality
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Where this data comes from
13 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_WQX13 samples · 2022
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)