Big Marsh Lake
Cook County, IllinoisView mapDirections
Not enough samples to grade — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). No letter yet. Here is what we do have.
- Impaired · Mercury
- Round Goby
- Limited data
Big Marsh Lake in Cook County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar.
- Trend
- ↓ Declining
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Stays near Big Marsh Lake
Compare lakeside cabins, hotels, and vacation rentals near Big Marsh 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.
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Watch Big Marsh Lake’s letter
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Why Big Marsh Lake has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Big Marsh Lake, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by Illinois EPA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Big Marsh Lake is a lake in Cook County, Illinois. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2023-04-26. Grade methodology: LakeQuality methodology.
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Big Marsh Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pesticides, pCBs. Check local advisories before you swim.
Water quality measurements for Big Marsh Lake
These readings exist but are not enough for an A–F grade — see why.
No clarity data.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples |
Fishing Big Marsh 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 | -22.5 m/yr | 2 |
EPA Impairment Status
Big Marsh 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_RHO · Official waterbody report · Matched by proximity (1.71 km)
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Big Marsh Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Cargill Industrial SpecialitiesChicago · 1.4 mi away · NPDES IL0056057Recent violation
- Pvs Chemical Solutions IncChicago · 1.6 mi away · NPDES IL0002640Recent violation
- Land&Lakes CompanyChicago · 0.2 mi away · NPDES IL0067237
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.
Graded lakes near Big Marsh Lake
Big Marsh Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Cook County
Frequently asked questions about Big Marsh Lake
Where is Big Marsh Lake?
- Big Marsh Lake is a lake in Cook County, Illinois. LakeQuality has not rated this lake (UNRATED) — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
What is the water quality grade for Big Marsh Lake?
- Big Marsh Lake in Cook County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar.
Is Big Marsh Lake safe to swim in?
- The letter is not a swimming clearance. Big Marsh Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pesticides, pCBs. Check local advisories before you swim.
Explore Big Marsh Lake across LakeQuality
Planning a trip around Indiana Dunes?
Big Marsh 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 Lakes in Illinois
Where this data comes from
1 measurement from 1 monitoring station, 2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Illinois Water Science Center
USGS-IL1 sample · 2023
Analytical methods
- Secchi disk method
Monitoring station identifiers (1)
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)