Flatfoot Lake is a productive, nutrient-rich eutrophic lake in Cook County, Illinois. Water quality is graded D based on 1 sampling years through 2022. Overall water quality is declining 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, Flatfoot Lake ranks #19 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2022-09-01. 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
Murky, only visible to about 6 ft. Trophic State Index: 51.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Flatfoot Lake
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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 |
Recreation & Access
Water Temperature
Flatfoot Lake averages about 78°F at the surface in summer, 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 →
Location
County Ranking
Ranked #19 of 68 lakes in Cook County
Cleaner Lakes Within 30 Miles
Flatfoot Lake holds Grade D. 3 nearby lakes hold higher grades.
Nearby Lakes in Cook County
Explore Flatfoot 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
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.
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: 2022-09-01
Monitoring stations: 1