Mcgilvray Lake
Flathead County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Mcgilvray Lake. Here is what has been measured.
- Oligotrophic
Mcgilvray Lake in Flathead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 5.9 µg/L. Chlorophyll-a (algae): 1.7 µg/L.
Mcgilvray Lake is a cold, clear oligotrophic lake in Flathead County, Montana. Overall water quality is declining over recent sampling years. Compared to the 43 other monitored lakes in Flathead County, Mcgilvray Lake ranks #25 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2023-08-03. Methodology: how these readings are compared.
Swimming conditions
Readings onlyModerate algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Mcgilvray 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 Mcgilvray Lake
These are the measurements Montana DEQ publishes for Mcgilvray 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 5.9 µg/L. Chlorophyll-a 1.7 µg/L. TSI 33.
| 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 | 5.9µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 1.7µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 33 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
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Fishing Mcgilvray Lake
Water Quality Trend: Worsening
Based on 11 years of monitoring (2012–2023).
Water clarity
Stable3 years
Phosphorus
Worsening+0.81 µg/L/yr10 years
Chlorophyll-a
Worsening+0.19 µg/L/yr11 years
Nearby Lakes in Flathead County
Frequently asked questions about Mcgilvray Lake
Where is Mcgilvray Lake?
- Mcgilvray 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 Mcgilvray Lake?
- Mcgilvray Lake in Flathead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 5.9 µg/L. Chlorophyll-a (algae): 1.7 µg/L.
Is Mcgilvray Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Mcgilvray Lake across LakeQuality
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Other Lakes in Montana
Oligotrophic Lakes in Montana
Where this data comes from
25 measurements from 1 monitoring station, 2012–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana Watershed
MTWTRSHD_WQX25 samples · 2012–2023
Analytical methods
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 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.