Is Lake Butte des Morts Polluted?
Yes — Lake Butte des Morts in Winnebago County, Wisconsin is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity. 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 | Winnebago County, Wisconsin |
Pollutants Cited
- Cause unknown — listed by EPA as exceeding water-quality standards for at least one designated use.
- 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.
- Turbidity — listed by EPA as exceeding water-quality standards for at least one designated use.
Specific parameters in the EPA record: CAUSE UNKNOWN, PHOSPHORUS, TOTAL, TOTAL SUSPENDED SOLIDS (TSS).
What this means for using Lake Butte des Morts
Because Lake Butte des Morts 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 Butte des Morts carries an overall water-quality grade of F — see the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.