Is Lac Courte Oreilles Lake Polluted?
Yes — Lac Courte Oreilles Lake in Sawyer County, Wisconsin is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Cause unknown. 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 | Sawyer County, Wisconsin |
Pollutants Cited
- Cause unknown — listed by EPA as exceeding water-quality standards for at least one designated use.
Specific parameters in the EPA record: CAUSE UNKNOWN.
What this means for using Lac Courte Oreilles Lake
Review the EPA assessment and any state advisories before relying on Lac Courte Oreilles Lake for swimming, fishing, or other uses. 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. Lac Courte Oreilles Lake carries an overall water-quality grade of A, with algae (chlorophyll-a) at 1.4 µg/L and phosphorus at 16 µg/L — see the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.