Lake Mcdonald
Flathead County, MontanaView mapDirections
Not enough samples to grade — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). No letter yet. Here is what we do have.
- Limited data
Lake Mcdonald in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Chlorophyll-a (algae): 0.7 µg/L.
- Chlorophyll-a
- 0.7 µg/L
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Stays near Lake Mcdonald
Compare lakeside cabins, hotels, and vacation rentals near Lake Mcdonald in Flathead County, Montana — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
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Watch Lake Mcdonald’s letter
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Why Lake Mcdonald has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Lake Mcdonald, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded algae (chlorophyll-a), but not water clarity and phosphorus.
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by Montana DEQ and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Lake Mcdonald is a lake in Flathead County, Montana.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2018-07-19. Grade methodology: LakeQuality methodology.
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for Lake Mcdonald
These readings exist but are not enough for an A–F grade — see why.
No clarity data. Chlorophyll-a 0.7 µg/L. TSI 27.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 0.7 µg/L | Not graded |
| Trophic State Index (TSI) | 27 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Fishing Lake Mcdonald
Graded lakes near Lake Mcdonald
Lake Mcdonald has no grade, but these lakes within a short drive do.
Nearby Lakes in Flathead County
Frequently asked questions about Lake Mcdonald
Where is Lake Mcdonald?
- Lake Mcdonald is a lake in Flathead County, Montana. LakeQuality has not rated this lake (UNRATED) — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
What is the water quality grade for Lake Mcdonald?
- Lake Mcdonald in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Chlorophyll-a (algae): 0.7 µg/L.
Is Lake Mcdonald safe to swim in?
- The letter is 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 Montana Lake Rankings
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)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.