Lily Lake is a productive, nutrient-rich eutrophic lake in McHenry County, Illinois. Water quality is graded B based on 2 sampling years through 2021. Limited fish-species data available. Public access is available with 1 public boat landing. 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 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
Very murky, less than 3.3 ft of visibility. Phosphorus level: 16 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.3 ft | D |
| Phosphorus | 16 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Lily Lake
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Fishing Lily Lake
Recreation & Access
Water Temperature
Lily Lake averages about 73°F at the surface in summer, 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 →
Location
County Ranking
Ranked #3 of 5 lakes in McHenry County
Cleaner Lakes Within 30 Miles
Lily Lake holds Grade B. 2 nearby lakes hold higher grades.
- BSilver LakeMcHenry County · 6.2 mi · Higher overall water quality score
- BRound LakeLake County · 7 mi · Higher overall water quality score
Nearby Lakes in McHenry County
Explore Lily 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
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
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
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.
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