Flatfoot Lake
Cook County, IllinoisView mapDirections
Nutrients and algae run above the regional average.
- Eutrophic
- Impaired · Mercury
- Round Goby
- #6 of 16 in the county
- Public access
- Limited data
Flatfoot Lake in Cook County, Illinois has a water quality grade of D (Nutrient-rich). Water clarity: 6.2 ft visibility. Phosphorus: 18 µg/L. Chlorophyll-a (algae): 21.3 µg/L.
- Clarity
- 6.2 ft
- Typical in September
- 78°F
- Type
- Eutrophic
- Phosphorus
- 18 µg/L
- Chlorophyll-a
- 21.3 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
Stays via Stay22
Stays near Flatfoot Lake
Compare lakeside cabins, hotels, and vacation rentals near Flatfoot 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 Flatfoot Lake are listed below.
Top-rated places to stay near Flatfoot Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
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Watch Flatfoot Lake’s letter
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Flatfoot Lake is a productive, nutrient-rich eutrophic lake in Cook County, Illinois. Water quality is graded D based on 2 sampling years through 2022. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 15 other monitored lakes in Cook County, Flatfoot Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2022-09-01. Grade methodology: LakeQuality methodology.
What Flatfoot Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
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. Flatfoot Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Murky, only visible to about 6.2 ft. Phosphorus 18 µg/L. Chlorophyll-a 21.3 µg/L. TSI 52. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.2 ft | Not graded |
| Phosphorus | 18 µg/L | Good |
| Chlorophyll-a (Algae) | 21.3 µg/L | Poor |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Flatfoot Lake typically sits around 78°F at the surface in September. Summer average is about 78°F. Usually warmest in Jul (about 81°F) and coldest in Oct (about 60°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 58 field readings (2016–2022) via the EPA Water Quality Portal. See the full Flatfoot Lake water temperature breakdown →
Recreation & Access
- Beaubien Woods - 2Public
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Flatfoot Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Source: USGS Nonindigenous Aquatic Species (NAS) Database. Hover a chip to see scientific name, ecological context, status, and first-observed year.
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -35 m/yr | 2 |
EPA Impairment Status
Flatfoot 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_RHZJ · Official waterbody report
Regulated Pollution Sources Nearby
6 EPA-permitted facilities operate within about 5 miles of Flatfoot Lake under Clean Water Act (NPDES) discharge permits. 3 facilities have a reported Clean Water Act violation in the past three years.
- River Bend Prairie LandfillDolton · 1.2 mi away · NPDES IL0075566Recent violation
- Phoenix Csos, Village OfPhoenix · 3.1 mi away · NPDES IL0072834Recent violation
- Indiana Harbor Belt RailroadRiverdale · 3.2 mi away · NPDES IL0062863Recent violation
- Riverdale Industries, Inc.Riverdale · 1.8 mi away · NPDES IL0068926
- Mittal Steel Usa-RiverdaleRiverdale · 2.3 mi away · NPDES IL0076295
- Hammond Pipeline Relocation ProjectRiverdale · 3.8 mi away · NPDES IL0080097
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 #6 of 16 lakes in Cook County
Nearby Lakes With Higher Grades
Flatfoot Lake holds Grade D. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Cook County
Frequently asked questions about Flatfoot Lake
Where is Flatfoot Lake?
- Flatfoot Lake is a lake in Cook County, Illinois. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Flatfoot Lake?
- Flatfoot Lake in Cook County, Illinois has a water quality grade of D (Nutrient-rich). Water clarity: 6.2 ft visibility. Phosphorus: 18 µg/L. Chlorophyll-a (algae): 21.3 µg/L.
Is Flatfoot Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Flatfoot Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
What is the water temperature of Flatfoot Lake?
- Flatfoot Lake typically sits around 78°F at the surface in September, from 58 EPA Water Quality Portal field readings (2016–2022). That is a typical value for the month, not a live reading.
Are there boat ramps on Flatfoot Lake?
- Flatfoot Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Beaubien Woods - 2. Public access is listed as yes.
Explore Flatfoot Lake across LakeQuality
Planning a trip around Indiana Dunes?
Flatfoot Lake is about 25 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 D Lakes in Illinois
Eutrophic Lakes in Illinois
Where this data comes from
37 measurements from 3 monitoring stations, 2020–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX36 samples · 2020 - USGS Illinois Water Science Center
USGS-IL1 sample · 2022
Analytical methods
- Secchi disk method
- 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)
Named boat-access points from the USGS National Boat Ramps inventory