Is Mormon Trail Lake Polluted?
Yes — Mormon Trail Lake in Adair County, Iowa is on the EPA's Clean Water Act 303(d) impaired-waters list (2024 assessment cycle). It is cited for Mercury. 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 | Adair County, Iowa |
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.
Specific parameters in the EPA record: MERCURY - FISH CONSUMPTION ADVISORY.
What this means for using Mormon Trail Lake
Mormon Trail Lake's listing is driven by contaminants that build up in fish (Mercury), so the practical impact is on eating the fish, not on swimming. Follow the state fish-consumption advisory for Iowa. 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. Mormon Trail Lake carries an overall water-quality grade of C, with algae (chlorophyll-a) at 9.7 µg/L — see the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.