Mcgilvray Lake
Flathead County, MontanaView mapDirections
Not Rated: one monitoring station are on record, but they measured water clarity only. LakeQuality’s A–F method grades total phosphorus, total nitrogen, chlorophyll-a, and turbidity; clarity is shown, not scored.
- Limited data
Mcgilvray Lake in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 21 ft visibility.
- Clarity
- 21 ft
- Trend
- ↓ Declining
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Watch Mcgilvray Lake’s letter
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Why Mcgilvray Lake has no grade
Mcgilvray Lake has monitoring on record from one station, but only water clarity was measured. LakeQuality’s A–F letter uses total phosphorus, total nitrogen, chlorophyll-a, and turbidity against EPA National Lakes Assessment condition classes. With none of those grading measurements on record, Mcgilvray Lake is Not Rated — not an F. Its 21-foot median from 3 readings collected 2020–2023 is still shown as clarity, but clarity alone cannot earn a letter.
Not Rated is EPA Integrated Reporting Category 3 — insufficient information. 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.
Mcgilvray 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 2023-08-03. Grade methodology: LakeQuality methodology.
What Mcgilvray Lake is good for
From access and monitoring records, not editorial picks.
- Clear water21 ft of visibility
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for Mcgilvray Lake
These readings exist but are not enough for an A–F grade — see why.
Crystal clear, you can see 21 ft down. TSI 33.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 21 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 33 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Fishing Mcgilvray Lake
Water Quality Trend: ↓ Declining
Based on 11 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.011 m/yr | 3 |
| Phosphorus | ↓ Declining | +0.81 µg/L/yr | 10 |
| Chlorophyll-a | ↓ Declining | +0.19 µg/L/yr | 11 |
Graded lakes near Mcgilvray Lake
Mcgilvray Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Flathead County
Frequently asked questions about Mcgilvray Lake
Where is Mcgilvray Lake?
- Mcgilvray Lake is a lake in Flathead County, Montana. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Mcgilvray Lake?
- Mcgilvray Lake in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 21 ft visibility.
Is Mcgilvray Lake safe to swim in?
- The letter is not a swimming clearance. Check local advisories before you swim.
Explore Mcgilvray Lake across LakeQuality
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Where this data comes from
3 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North American Lake Management Society
NALMS3 samples · 2020–2023
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.