Is Lower Prior Lake Polluted?
Yes — Lower Prior Lake in Scott 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. 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 | Scott 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.
Specific parameters in the EPA record: FISH BIOASSESSMENTS, MERCURY IN FISH TISSUE.
What this means for using Lower Prior Lake
Lower Prior 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 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. Lower Prior Lake carries an overall water-quality grade of B and phosphorus at 26.8 µg/L — see the full breakdown on the lake report. The official EPA assessment is available in the ATTAINS waterbody report.