Is Thread Lake Central Basin Polluted?
Yes — Thread Lake Central Basin in Genesee County, Michigan is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Nutrients (phosphorus, nitrogen), 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 | Genesee County, Michigan |
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.
- 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: EUTROPHICATION, NUTRIENTS, PCBS IN FISH TISSUE, TROPHIC STATE INDEX (TSI).
What this means for using Thread Lake Central Basin
Because Thread Lake Central Basin 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. Thread Lake Central Basin carries an overall water-quality grade of C, with algae (chlorophyll-a) at 7.6 µg/L — see the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.