Little Grassy Lake
Williamson County, Illinois905 acresView mapDirections
No nutrient or algae sampling on record from Illinois EPA for this lake.
- Impaired · Mercury
- 65 ft max depth
Little Grassy Lake in Williamson County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Maximum depth: 65 ft. Surface area: 905 acres.
Little Grassy Lake is a 905-acre lake in Williamson County, Illinois with a maximum depth of 65 feet (26-foot average).
Source: EPA Water Quality Portal sampling records, Illinois EPA. Methodology: how these readings are compared.
What Little Grassy Lake is good for
From access and monitoring records, not editorial picks.
- Deep water65 ft surveyed max depth
Swimming conditions
No readingNot rated
Nutrient and algae readings are not a swimming clearance. Little Grassy Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Whether Little Grassy Lake 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 Little Grassy Lake
These are the measurements Illinois EPA publishes for Little Grassy Lake, 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 Little Grassy Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
65 ft
Average depth
25.7 ft
Surface area
905 acres
Shoreline
26 mi
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Stays near Little Grassy Lake
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Fishing Little Grassy Lake
EPA Impairment Status
Little Grassy Lake 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.
Source: EPA ATTAINS assessment unit IL_RNK · Official waterbody report
Nearby Lakes in Williamson County
Frequently asked questions about Little Grassy Lake
Where is Little Grassy Lake?
- Little Grassy Lake 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 Little Grassy Lake?
- Little Grassy Lake in Williamson County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Maximum depth: 65 ft. Surface area: 905 acres.
Is Little Grassy Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Little Grassy Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
How deep is Little Grassy Lake?
- Little Grassy Lake has a maximum depth of 65 feet and an average depth of 25.7 feet. The lake covers 905 acres.
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Where this data comes from
Measurements for Little Grassy Lake 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