Lake Mcdonald
Flathead County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Lake Mcdonald. Here is what has been measured.
- Limited data
Lake Mcdonald in Flathead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Chlorophyll-a (algae): 0.7 µg/L.
Lake Mcdonald is a lake in Flathead County, Montana.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2018-07-19. Methodology: how these readings are compared.
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Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Lake Mcdonald 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 Lake Mcdonald
These are the measurements Montana DEQ publishes for Lake Mcdonald, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Chlorophyll-a 0.7 µg/L. TSI 27.
| 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 | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | 0.7µg/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. | 27 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
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Frequently asked questions about Lake Mcdonald
Where is Lake Mcdonald?
- Lake Mcdonald 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 Lake Mcdonald?
- Lake Mcdonald in Flathead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Chlorophyll-a (algae): 0.7 µg/L.
Is Lake Mcdonald safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Lake Mcdonald across LakeQuality
Planning a trip around Glacier?
Lake Mcdonald is about 10 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
Other Lakes in Montana
Oligotrophic Lakes in Montana
Where this data comes from
2 measurements from 1 monitoring station, 2018. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- National Park Service Water Resources Division
11NPSWRD_WQX2 samples · 2018
Analytical methods
- 10200 H ~ Chlorophyll a-b-c Determination
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.