Williamson Reservoir is a highly nutrient-loaded hypereutrophic lake in Chouteau County, Montana. Water quality is graded C based on 2 sampling years through 2022. Compared to the 2 other monitored lakes in Chouteau County, Williamson Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DNR, last sampled 2022-09-20. Grade methodology: LakeGrade methodology.
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
No clarity data. Phosphorus level: 410 µg/L. Chlorophyll-a: 6.7 µg/L. Trophic State Index: 70.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | 410 µg/L | F |
| Chlorophyll-a (Algae) | 6.7 µg/L | B |
| Trophic State Index (TSI) | 70 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Williamson Reservoir
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Fishing Williamson Reservoir
Location
County Ranking
Ranked #1 of 3 lakes in Chouteau County
Nearby Lakes in Chouteau County
Explore Williamson Reservoir across LakeGrade
More Montana Lake Rankings
Other Grade C Lakes in Montana
More records, surveys & data sources
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-09-20
Monitoring stations: 1