Is Mattoon Lake Polluted?
Yes — Mattoon Lake in Cumberland County, Illinois is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Algal growth, Mercury, Nutrients (phosphorus, nitrogen), Pesticides, Turbidity. A formal cleanup plan — a Total Maximum Daily Load (TMDL) — has been written. "Impaired" is a legal designation, separate from the lake's EPA condition class water-quality readings: 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 |
| Uses not supported | Drinking water, Fish consumption, Other |
| EPA names this lake in the listing | Yes |
| Location | Cumberland County, Illinois |
Pollutants Cited
- Algal growth — listed by EPA as exceeding water-quality standards for at least one designated use.
- Mercury — Mercury accumulates in fish tissue and is the single most common impairment in northern lakes. It usually arrives via atmospheric deposition from coal combustion rather than local discharge — which is why even remote, clear lakes can be mercury-impaired. It triggers fish-consumption advisories, not swimming closures.
- 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.
- Turbidity — listed by EPA as exceeding water-quality standards for at least one designated use.
Specific parameters in the EPA record: Algae, Atrazine, Mercury, Phosphorus, Total, Simazine, Total Suspended Solids (TSS).
What this means for using Mattoon Lake
Because Mattoon Lake 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. Mattoon Lake measures algae (chlorophyll-a) at 87.1 µg/L and phosphorus at 294 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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