Is Lake Washington Polluted?
Yes — Lake Washington in King County, Washington is on the EPA's Clean Water Act 303(d) impaired-waters list (2018 assessment cycle). It is cited for Mercury, PCBs. No cleanup plan (TMDL) has been completed yet. "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) | Not yet written |
| Assessment cycle | 2018 |
| EPA IR category | 5 |
| Uses not supported | Fish consumption |
| EPA names this lake in the listing | Yes |
| Location | King County, Washington |
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.
- 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: Methylmercury in Fish Tissue, PCBs in Fish Tissue.
What this means for using Lake Washington
Lake Washington's listing is driven by contaminants that build up in fish (Mercury, PCBs), so the practical impact is on eating the fish, not on swimming. Follow the state fish-consumption advisory for Washington. 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. See the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.
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