Lily Lake
McHenry County, IllinoisView mapDirections
Nutrients and algae run above the regional average.
↓ down from B at the last regrade
- Eutrophic
- Impaired · Noxious aquatic plants
- #3 of 5 in the county
- 36 ft max depth
- Public access
- Limited data
Lily Lake in McHenry County, Illinois has a water quality grade of D (Nutrient-rich). Water clarity: 3.3 ft visibility. Phosphorus: 19 µg/L. Chlorophyll-a (algae): 25.4 µg/L.
- Clarity
- 3.3 ft
- Typical in August
- 76°F
- Max depth
- ~36 ft est.
- Type
- Eutrophic
- Phosphorus
- 19 µg/L
- Chlorophyll-a
- 25.4 µg/L
- Public access
- Yes
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Stays near Lily Lake
Compare lakeside cabins, hotels, and vacation rentals near Lily Lake in McHenry 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Lily Lake are listed below.
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Lily Lake is a productive, nutrient-rich eutrophic lake in McHenry County, Illinois with an estimated average depth of about 36 feet. Water quality is graded D based on 2 sampling years through 2021. Limited fish-species data available. Public access is available. Compared to the 4 other monitored lakes in McHenry County, Lily Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2021-10-12. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The D is nutrients and algae, not a swimming clearance. Lily Lake is listed impaired under Clean Water Act §303(d) (IR 5) for noxious aquatic plants, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 3.3 ft of visibility. Phosphorus 19 µg/L. Chlorophyll-a 25.4 µg/L. TSI 56. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.3 ft | Not graded |
| Phosphorus | 19 µg/L | Good |
| Chlorophyll-a (Algae) | 25.4 µg/L | Poor |
| Trophic State Index (TSI) | 56 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Lily Lake typically sits around 76°F at the surface in August. Summer average is about 73°F. Usually warmest in Aug (about 76°F) and coldest in Oct (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 160 field readings (2012–2021) via the EPA Water Quality Portal. See the full Lily Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~36 ft est. |
| Average Depth | ~9 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Lily 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 Lily Lake
EPA Impairment Status
Lily 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_RTZJ · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Lily Lake under Clean Water Act (NPDES) discharge permits, including 2 classified by the EPA as major dischargers. 1 facility has a reported Clean Water Act violation in the past three years.
- Mchenry - South WwtpMchenry · 2.6 mi away · NPDES IL0066257MajorRecent violation
- City Of Mchenry - Central WwtpMchenry · 3 mi away · NPDES IL0021067Major
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.
County Ranking
Ranked #3 of 5 lakes in McHenry County
Nearby Lakes in McHenry County
Frequently asked questions about Lily Lake
Where is Lily Lake?
- Lily Lake is a lake in McHenry County, Illinois. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lily Lake?
- Lily Lake in McHenry County, Illinois has a water quality grade of D (Nutrient-rich). Water clarity: 3.3 ft visibility. Phosphorus: 19 µg/L. Chlorophyll-a (algae): 25.4 µg/L.
Is Lily Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Lily Lake is listed impaired under Clean Water Act §303(d) (IR 5) for noxious aquatic plants, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Lily Lake?
- Lily Lake typically sits around 76°F at the surface in August, from 160 EPA Water Quality Portal field readings (2012–2021). That is a typical value for the month, not a live reading.
How deep is Lily Lake?
- No published bathymetric survey covers Lily Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 36 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Lily Lake across LakeQuality
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Where this data comes from
52 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_WQX52 samples · 2021
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (3)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)