Marion Reservoir
Marion Reservoir in Williamson County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 245 acres.
- Area
- 245 acres
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Why Marion Reservoir 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 Marion Reservoir, 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.
Marion Reservoir is a 245-acre lake in Williamson County, Illinois.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled recent years. Grade methodology: LakeQuality methodology.
Watch Marion Reservoir 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 Marion Reservoir
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 Marion Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Marion Reservoir in Williamson 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 Marion Reservoir
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 245 acres |
No bathymetric survey has been published for Marion Reservoir, so its depth is not documented here.
Fishing Marion Reservoir
Nearby Lakes in Williamson County
Frequently asked questions about Marion Reservoir
Where is Marion Reservoir?
- Marion Reservoir is a lake in Williamson 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 Marion Reservoir?
- Marion Reservoir in Williamson County, Illinois is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 245 acres.
Is Marion Reservoir safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Marion Reservoir is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Explore Marion Reservoir across LakeQuality
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Where this data comes from
Measurements for Marion Reservoir come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.