Is Clear Lake Polluted?
Yes — Clear Lake in Washington County, Minnesota is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Impaired biota (cause unknown), Mercury, PFAS. 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 | Aquatic life, Fish consumption |
| EPA names this lake in the listing | Yes |
| Location | Washington County, Minnesota |
Pollutants Cited
- Impaired biota (cause unknown) — 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.
- PFAS — Per- and polyfluoroalkyl "forever chemicals" from industrial and firefighting-foam sources. PFAS listings are newer and typically trigger fish-consumption and, in some cases, drinking-water guidance.
Specific parameters in the EPA record: Fish Bioassessments, Mercury in Fish Tissue, Perfluorooctane Sulfonate (PFOS) in Fish Tissue.
What this means for using Clear Lake
Clear Lake's listing is driven by contaminants that build up in fish (Mercury, PFAS), so the practical impact is on eating the fish, not on swimming. Follow the state fish-consumption advisory for Minnesota. 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. Clear Lake measures algae (chlorophyll-a) at 6.9 µg/L and phosphorus at 33 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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