Is Lake Oswego Polluted?
Yes — Lake Oswego in Clackamas County, Oregon is on the EPA's Clean Water Act 303(d) impaired-waters list (2022 assessment cycle). It is cited for Algal growth, pH / acidity. 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 | 2022 |
| EPA IR category | 5 |
| Uses not supported | Drinking water, Aquatic life, Fish consumption, Recreation, Other |
| EPA names this lake in the listing | Yes |
| Location | Clackamas County, Oregon |
Pollutants Cited
- Algal growth — listed by EPA as exceeding water-quality standards for at least one designated use.
- pH / acidity — listed by EPA as exceeding water-quality standards for at least one designated use.
Specific parameters in the EPA record: Harmful Algal Blooms, pH.
What this means for using Lake Oswego
Review the EPA assessment and any state advisories before relying on Lake Oswego 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. See the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.
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