Flathead County, Montana · 48.13°N · Water Quality Report Card
Little Bitterroot Lake
Little Bitterroot Lake in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 3 µg/L. Chlorophyll-a (algae): 0.5 µg/L.
- Mean depth
- ~49 ft est.
- Type
- Oligotrophic
- Trend
- ↑ Improving
Little Bitterroot Lake is a cold, clear oligotrophic lake in Flathead County, Montana with an estimated average depth of about 49 feet. Overall water quality is improving over recent sampling years.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2024-10-05. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not rated for swimming — there is not enough monitoring data to judge this lake
Water Quality Grade: Not rated
No clarity data. Phosphorus level: 3 µg/L. Chlorophyll-a: 0.5 µg/L. Trophic State Index: 21.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | 3 µg/L | |
| Chlorophyll-a (Algae) | 0.5 µg/L | |
| Trophic State Index (TSI) | 21 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~49 ft est. |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Montana has not published bathymetry for Little Bitterroot Lake.
Where to stay near Little Bitterroot Lake
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Fishing Little Bitterroot Lake
Water Quality Trend: ↑ Improving
Based on 14 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +1.15 m/yr | 3 |
| Phosphorus | → Stable | -0.01 µg/L/yr | 14 |
| Chlorophyll-a | ↑ Improving | -0.06 µg/L/yr | 14 |
Location
Nearby Lakes in Flathead County
Explore Little Bitterroot Lake across LakeGrade
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Oligotrophic Lakes in Montana
More records, surveys & data sources
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Where this data comes from
12 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana Volunteer Water Quality Monitoring
MTVOLWQM_WQX12 samples · 2024
Analytical methods
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 4500 N C ~ Persufate Method for Total Nitrogen
Monitoring station identifiers (1)
Grade thresholds come from the U.S. EPA National Lakes Assessment 2022 Technical Support Document (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated.
Data Sources
Water quality data from the EPA Water Quality Portal
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion
Most recent sample: 2024-10-05
Monitoring stations: 1