Big Therriault Lake is a cold, clear oligotrophic lake in Lincoln County, Montana. Water quality is graded A based on 1 sampling years through 2023. Compared to the 25 other monitored lakes in Lincoln County, Big Therriault Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DNR, last sampled 2023-07-18. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 37.3 ft down. Trophic State Index: 25.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 37.3 ft | A |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 25 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Big Therriault Lake
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Fishing Big Therriault Lake
Location
County Ranking
Ranked #5 of 26 lakes in Lincoln County
Nearby Lakes in Lincoln County
Explore Big Therriault Lake across LakeGrade
More Montana Lake Rankings
Other Grade A Lakes in Montana
Flathead County · Clarity: 20.5 ft
Flathead County · Excellent
Flathead County · Excellent
Flathead County · Clarity: 21.9 ft
Flathead County · Clarity: 21 ft
Flathead County · Excellent
Oligotrophic 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: 2023-07-18
Monitoring stations: 1