Arrowhead Lake
Cook County, IllinoisView mapDirections
Nutrients and algae run well above the regional average.
↓ down from D at the last regrade
- Hypereutrophic
- Impaired · Cause unknown
- #12 of 16 in the county
- Public access
- Limited data
Arrowhead Lake in Cook County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 2.1 ft visibility. Phosphorus: 38 µg/L. Chlorophyll-a (algae): 37.6 µg/L.
- Clarity
- 2.1 ft
- Typical in September
- 77°F
- Type
- Hypereutrophic
- Phosphorus
- 38 µg/L
- Chlorophyll-a
- 37.6 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Stays near Arrowhead Lake
Compare lakeside cabins, hotels, and vacation rentals near Arrowhead Lake in Cook 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 Arrowhead Lake are listed below.
Top-rated places to stay near Arrowhead Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
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Arrowhead Lake is a highly nutrient-loaded hypereutrophic lake in Cook County, Illinois. Water quality is graded F 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. Compared to the 15 other monitored lakes in Cook County, Arrowhead Lake ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2020-10-05. 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 F is nutrients and algae, not a swimming clearance. Arrowhead Lake is listed impaired under Clean Water Act §303(d) (IR 5) for cause unknown, mercury. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 2.1 ft of visibility. Phosphorus 38 µg/L. Chlorophyll-a 37.6 µg/L. TSI 63. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.1 ft | Not graded |
| Phosphorus | 38 µg/L | Good |
| Chlorophyll-a (Algae) | 37.6 µg/L | Poor |
| Trophic State Index (TSI) | 63 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Arrowhead Lake typically sits around 77°F at the surface in September. Summer average is about 74°F. 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 →
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 |
| Chlorophyll-a | ↑ Improving | -13.2 µg/L/yr | 2 |
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.
County Ranking
Ranked #12 of 16 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Arrowhead Lake
Where is Arrowhead Lake?
- Arrowhead Lake is a lake in Cook County, Illinois. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Arrowhead Lake?
- Arrowhead Lake in Cook County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 2.1 ft visibility. Phosphorus: 38 µg/L. Chlorophyll-a (algae): 37.6 µg/L.
Is Arrowhead Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Arrowhead Lake is listed impaired under Clean Water Act §303(d) (IR 5) for cause unknown, mercury. Check local advisories before you swim.
What is the water temperature of Arrowhead Lake?
- Arrowhead Lake typically sits around 77°F at the surface in September, from 112 EPA Water Quality Portal field readings (2011–2022). That is a typical value for the month, not a live reading.
Explore Arrowhead Lake across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Illinois's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
Illinois's cleanest and most-polluted lakes, ranked
Planning a trip around Indiana Dunes?
Arrowhead Lake is about 36 miles from Indiana Dunes National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Indiana Dunes →More Illinois Lake Rankings
Other Grade F Lakes in Illinois
Hypereutrophic Lakes in Illinois
Where this data comes from
36 measurements from 2 monitoring stations, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX36 samples · 2020
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (2)
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)