Longjohn Slough
Longjohn Slough in Cook County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 53 acres.
- Area
- 53 acres
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Why Longjohn Slough 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 Longjohn Slough, no water-quality sampling on record for this lake.
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.
Longjohn Slough is a 53-acre lake in Cook County, Illinois.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled recent years. Grade methodology: LakeQuality methodology.
Watch Longjohn Slough water quality
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Swimming Safety
Not ratedElevated nutrients
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Longjohn Slough
These readings exist but are not enough for an A–F grade — see why.
No clarity data. Trophic State Index: undefined.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) |
Where to stay near Longjohn Slough
Compare lakeside cabins, hotels, and vacation rentals near Longjohn Slough 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.
Top-rated places to stay near Longjohn Slough
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 53 acres |
No bathymetric survey has been published for Longjohn Slough, so its depth is not documented here.
Fishing Longjohn Slough
Nearby Lakes in Cook County
Frequently asked questions about Longjohn Slough
Where is Longjohn Slough?
- Longjohn Slough is a lake in Cook County, Illinois. LakeQuality has not rated this lake (UNRATED) — no water-quality sampling on record for this lake.
What is the water quality grade for Longjohn Slough?
- Longjohn Slough in Cook County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 53 acres.
Is Longjohn Slough safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Longjohn Slough is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Explore Longjohn Slough across LakeQuality
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Where this data comes from
Measurements for Longjohn Slough come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.