Is Lake Orion Polluted?
Yes — Lake Orion in Oakland County, Michigan is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Mercury, Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO), Pesticides, PCBs. No cleanup plan (TMDL) has been completed yet. "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) | Not yet written |
| Assessment cycle | 2024 |
| EPA IR category | 5 |
| Location | Oakland County, Michigan |
Pollutants Cited
- 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.
- Oxygen depletion (low DO) — listed by EPA as exceeding water-quality standards for at least one designated use.
- 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: CHLORDANE, DISSOLVED OXYGEN, MERCURY IN FISH TISSUE, PCBS IN FISH TISSUE, PHOSPHORUS, TOTAL.
What this means for using Lake Orion
Because Lake Orion 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 Orion carries an overall water-quality grade of B — see the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.