Poss Lake is a productive, nutrient-rich eutrophic lake in DuPage County, Illinois. Water quality is graded D based on 2 sampling years through 2021.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2021-09-22. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 1.2 ft of visibility. Phosphorus level: 32 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.2 ft | F |
| Phosphorus | 32 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Poss Lake
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Fishing Poss Lake
Water Temperature
Poss Lake averages about 69°F at the surface in summer, usually warmest in Jul (about 73°F) and coldest in May (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 17 field readings (2021–2021) via the EPA Water Quality Portal. See the full Poss Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 1 lakes in DuPage County
Cleaner Lakes Within 30 Miles
Poss Lake holds Grade D. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in DuPage County
Explore Poss Lake across LakeGrade
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Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
Regulated Pollution Sources Nearby
13 EPA-permitted facilities operate within about 5 miles of Poss Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 6 facilities have a reported Clean Water Act violation in the past three years.
- Batavia Wwtf, City OfBatavia · 4.1 mi away · NPDES IL0022543MajorRecent violation
- Heartland Recycling - Aurora Ccdd LlcAurora · 3.2 mi away · NPDES IL0071820Recent violation
- Dart Container CorporationNorth Aurora · 3.8 mi away · NPDES IL0051381Recent violation
- Mooseheart-Child City And School-StpMooseheart · 3.8 mi away · NPDES IL0027260Recent violation
- FermilabBatavia · 4.1 mi away · NPDES IL0026123Recent violation
- Phillips Park Family Aquatics CenterAurora · 5 mi away · NPDES IL0075035Recent 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.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2021-09-22
Monitoring stations: 1