Lost Loon Lake
Flathead County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Lost Loon Lake. Here is what has been measured.
- Limited data
Lost Loon Lake in Flathead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 10.1 µg/L. Chlorophyll-a (algae): 2.6 µg/L.
Lost Loon Lake is a lake in Flathead County, Montana. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2023-08-07. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Lost Loon Lake is safe to swim in today is a call for the Montana Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Lost Loon Lake
These are the measurements Montana DEQ publishes for Lost Loon Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 10.1 µg/L. Chlorophyll-a 2.6 µg/L. TSI 39.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 10.1µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 2.6µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 39 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
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Fishing Lost Loon Lake
Water Quality Trend: Worsening
Based on 12 years of monitoring (2012–2023).
Water clarity
Stable3 years
Phosphorus
Worsening+0.32 µg/L/yr11 years
Chlorophyll-a
Worsening+0.04 µg/L/yr12 years
Nearby Lakes in Flathead County
Frequently asked questions about Lost Loon Lake
Where is Lost Loon Lake?
- Lost Loon Lake is a lake in Flathead County, Montana. Its water-quality measurements are published by Montana DEQ and shown on this page as reported.
What is the water quality of Lost Loon Lake?
- Lost Loon Lake in Flathead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 10.1 µg/L. Chlorophyll-a (algae): 2.6 µg/L.
Is Lost Loon Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Lost Loon Lake across LakeQuality
Planning a trip around Glacier?
Lost Loon Lake is about 32 miles from Glacier National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Glacier →More lakes in Montana
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Oligotrophic Lakes in Montana
Where this data comes from
6 measurements from 1 monitoring station, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana Watershed
MTWTRSHD_WQX6 samples · 2022–2023
Analytical methods
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 4500 N C ~ Persufate Method for Total Nitrogen
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.