Arrowhead Lake is a productive, nutrient-rich eutrophic lake in Cook County, Illinois. Water quality is graded D based on 2 sampling years through 2020. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 67 other monitored lakes in Cook County, Arrowhead Lake ranks #38 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2020-10-05. 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 2.1 ft of visibility. Phosphorus level: 31.5 µg/L. Trophic State Index: 60.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.1 ft | F |
| Phosphorus | 31.5 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Arrowhead Lake
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Fishing Arrowhead Lake
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +9 m/yr | 2 |
| Phosphorus | ↑ Improving | -11 µg/L/yr | 2 |
Recreation & Access
Water Temperature
Arrowhead Lake averages about 74°F at the surface in summer, usually warmest in Jul (about 78°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 112 field readings (2011–2022) via the EPA Water Quality Portal. See the full Arrowhead Lake water temperature breakdown →
Location
County Ranking
Ranked #38 of 68 lakes in Cook County
Cleaner Lakes Within 30 Miles
Arrowhead Lake holds Grade D. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Cook County
Explore Arrowhead Lake across LakeGrade
More Illinois Lake Rankings
Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
EPA Impairment Status
Arrowhead 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_RHZE · Official waterbody report · Matched by proximity (0.06 km)
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Arrowhead Lake under Clean Water Act (NPDES) discharge permits.
- West Shore Pipe Line Co-AlsipAlsip · 2.2 mi away · NPDES IL0077518
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)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2020-10-05
Monitoring stations: 2