Marion Reservoir
Williamson County, Illinois245 acresView mapDirections
No nutrient or algae sampling on record from Illinois EPA for this lake.
- Impaired · Mercury
- 18 ft max depth
Marion Reservoir in Williamson County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Maximum depth: 18 ft. Surface area: 245 acres.
Marion Reservoir is a 245-acre lake in Williamson County, Illinois with a maximum depth of 18 feet (9-foot average).
Source: EPA Water Quality Portal sampling records, Illinois EPA. Methodology: how these readings are compared.
Swimming conditions
No readingNot rated
Nutrient and algae readings are not a swimming clearance. Marion Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pesticides, turbidity. Check local advisories before you swim.
Whether Marion Reservoir is safe to swim in today is a call for the Illinois Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Marion Reservoir
These are the measurements Illinois EPA publishes for Marion Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. TSI undefined.
Ask about Marion Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
18 ft
Average depth
9 ft
Surface area
245 acres
Shoreline
5.7 mi
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Fishing Marion Reservoir
EPA Impairment Status
Marion Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Fish consumption, Other.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_RNL · Official waterbody report
Nearby Lakes in Williamson County
Frequently asked questions about Marion Reservoir
Where is Marion Reservoir?
- Marion Reservoir is a lake in Williamson County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Marion Reservoir?
- Marion Reservoir in Williamson County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Maximum depth: 18 ft. Surface area: 245 acres.
Is Marion Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Marion Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pesticides, turbidity. Check local advisories before you swim.
How deep is Marion Reservoir?
- Marion Reservoir has a maximum depth of 18 feet and an average depth of 9 feet. The lake covers 245 acres.
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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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database