Is Lake of Egypt Polluted?
Yes — Lake of Egypt in Williamson County, Illinois is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Nutrients (phosphorus, nitrogen), Pesticides, PCBs. A formal cleanup plan — a Total Maximum Daily Load (TMDL) — has been written. "Impaired" is a legal designation, separate from the lake's A–F water-quality grade: it means at least one designated use (such as swimming, aquatic life, or fish consumption) does not meet state standards for the listed pollutant.
EPA 303(d) Listing
| On 303(d) impaired list | Yes |
| Cleanup plan (TMDL) | Completed |
| Assessment cycle | 2024 |
| EPA IR category | 5 |
| Location | Williamson County, Illinois |
Pollutants Cited
- Nutrients (phosphorus, nitrogen) — Excess phosphorus and nitrogen fuel algae growth and summer blooms. This is the classic agricultural-runoff and shoreline-development impairment, and the one most likely to affect swimming via blue-green algae.
- Pesticides — listed by EPA as exceeding water-quality standards for at least one designated use.
- PCBs — Polychlorinated biphenyls are legacy industrial pollutants that persist in sediment and bioaccumulate in fish. Like mercury, PCB listings drive fish-consumption advisories.
Specific parameters in the EPA record: ALDRIN, DIELDRIN, ENDRIN, HEPTACHLOR, MIREX, PHOSPHORUS, TOTAL, POLYCHLORINATED BIPHENYLS (PCBS), TOXAPHENE.
What this means for using Lake of Egypt
Because Lake of Egypt is listed for Nutrients (phosphorus, nitrogen), swimming can be affected — check for posted beach advisories, especially after heavy rain or during visible algae. An impairment listing does not mean the lake is closed — most impaired lakes remain open for boating and swimming. It means a specific pollutant exceeds a standard for a specific use. Lake of Egypt carries an overall water-quality grade of D, with algae (chlorophyll-a) at 22.1 µg/L and phosphorus at 40.5 µg/L — see the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.
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